Nonvolatile nanotube diodes and nonvolatile nanotube blocks and systems using same and methods of making same

ABSTRACT

Under one aspect, a nonvolatile nanotube diode includes: a substrate; a semiconductor element disposed over the substrate, the semiconductor element having an anode and a cathode and capable of forming an electrically conductive pathway between the anode and the cathode; a nanotube switching element disposed over the semiconductor element, the nanotube switching element including a conductive contact and a nanotube fabric element capable of a plurality of resistance states; and a conductive terminal disposed in spaced relation to the conductive contact, wherein the nanotube fabric element is interposed between and in electrical communication with the conductive contact and the conductive contact is in electrical communication with the cathode, and wherein in response to electrical stimuli applied to the anode and the conductive terminal, the nonvolatile nanotube diode is capable of forming an electrically conductive pathway between the anode and the conductive terminal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of thefollowing applications, the entire contents of which are incorporatedherein by reference:

U.S. Provisional Patent Application No. 60/855,109, entitled“Nonvolatile Nanotube Blocks,” filed on Oct. 27, 2006;

U.S. Provisional Patent Application No. 60/840,586, entitled“Nonvolatile Nanotube Diode,” filed on Aug. 28, 2006;

U.S. Provisional Patent Application No. 60/836,437, entitled“Nonvolatile Nanotube Diode,” filed on Aug. 8, 2006;

U.S. Provisional Patent Application No. 60/836,343, entitled “ScalableNonvolatile Nanotube Switches as Electronic Fuse Replacement Elements,”filed on Aug. 8, 2006; and

U.S. Provisional Patent Application No. 60/918,388, entitled “MemoryElements and Cross Point Switches and Arrays of Same Using NonvolatileNanotube Blocks,” filed on Mar. 16, 2007.

This application is a continuation-in-part of and claims priority under35 U.S.C. § 120 to the following applications, the entire contents ofwhich are incorporated by reference:

U.S. patent application Ser. No. 11/280,786, entitled “Two-TerminalNanotube Devices And Systems And Methods Of Making Same,” filed Nov. 15,2005;

U.S. patent application Ser. No. 11/274,967, entitled “Memory ArraysUsing Nanotube Articles With Reprogrammable Resistance,” filed Nov. 15,2005; and

U.S. patent application Ser. No. 11/280,599, entitled “Non-VolatileShadow Latch Using A Nanotube Switch,” filed Nov. 15, 2005.

This application is related to the following applications filedconcurrently herewith, the entire contents of which are incorporated byreference:

U.S. patent application Ser. No. (TBA), entitled “Nonvolatile ResistiveMemories Having Scalable Two-Terminal Nanotube Switches;”

U.S. patent application Ser. No. (TBA), entitled “Latch Circuits andOperation Circuits Having Scalable Nonvolatile Nanotube Switches asElectronic Fuse Replacement Elements;”

U.S. patent application Ser. No. (TBA), entitled “Memory Elements andCross Point Switches and Arrays of Same Using Nonvolatile NanotubeBlocks;”

U.S. patent application Ser. No. (TBA), entitled “Nonvolatile NanotubeDiodes and Nonvolatile Nanotube Blocks and Systems Using Same andMethods of Making Same;”

U.S. patent application Ser. No. (TBA), entitled “Nonvolatile NanotubeDiodes and Nonvolatile Nanotube Blocks and Systems Using Same andMethods of Making Same;”

U.S. patent application Ser. No. (TBA), entitled “Nonvolatile NanotubeDiodes and Nonvolatile Nanotube Blocks and Systems Using Same andMethods of Making Same;”

U.S. patent application Ser. No. (TBA), entitled “Nonvolatile NanotubeDiodes and Nonvolatile Nanotube Blocks and Systems Using Same andMethods of Making Same;” and

U.S. patent application Ser. No. (TBA), entitled “Nonvolatile NanotubeDiodes and Nonvolatile Nanotube Blocks and Systems Using Same andMethods of Making Same.”

TECHNICAL FIELD

The present invention relates to nonvolatile switching devices havingnanotube components and methods of forming such devices.

DISCUSSION OF RELATED ART

There is an ever-increasing demand for ever-denser memories that enablelarger memory functions, both stand alone and embedded, ranging from100's of kbits to memories in excess of 1 Gbit. These required largermemories at increasingly higher densities, sold in increasing volumes,and at lower cost per bit, are challenging the semiconductor industry torapidly improve geometries and process features. For example, suchdemands drive photolithography technology to smaller line and spacingdimensions with corresponding improved alignment between layers,improved process features/structures such as smaller transistors andstorage elements, but also including increased chip size required toaccommodate larger memory function, or combined memory and logicfunction. Sensitivity to smaller defect size increases due to thesmaller geometries, while overall defect densities must be significantlyreduced.

When transitioning to a new denser technology node, lithography andcorresponding process changes typically result in insulator andconductor dimensional reduction of 0.7× in the X and Y directions, or anarea reduction of 2× for logic circuits and memory support circuits.Process features unique to the memory cell are typically added,resulting in an additional typical 0.7× area reduction beyond the areareduction resulting from photolithographic improvements, such that thememory cell achieves a cell area reduction of approximately 2.8×. InDRAMs, for example, a process feature change such as a buried trench orstacked storage capacitor is introduced with corresponding optimizedcell contact means between one capacitor plate and the source of a cellselect FET formed in the semiconductor substrate. The tradeoffsdescribed with respect to DRAM memories are similar to those for othermemory types such as EPROM, EEPROM, and Flash.

Memory efficiency is determined by comparing the bit storage area andthe corresponding overhead of the support circuit area. Support circuitarea is minimized with respect to array storage area. For 2-D memories,that is memories in which a cell select transistor is formed in asemiconductor substrate, for a transition to a denser new technologynode (technology generation) the bit area may be reduced by more thanthe support circuit area as illustrated further above with respect to amemory example where the bit area is reduced by 2.8× while the supportcircuit area is reduced by 2×. In order to preserve memory efficiency,memory architecture may be changed such that larger sub-arrays arefabricated, that is sub-arrays with more bits per word line and morebits per bit line. In order continue to improve memory performance whilecontaining power dissipation, new memory architectures use global andlocal (segmented) word line and global and local (segmented) bit linearchitectures to accommodate larger sub-arrays with more bits per wordand bit lines as described for example in U.S. Pat. No. 5,546,349, theentire contents of which are incorporated herein by reference.

In addition to the growth in memory sub-array size, chip area may growas well. For example, if the memory function at a new technology node isto have 4× more bits, then if the bit area reduction is 2.8×, chip areagrowth will be at least 1.4-1.5×.

Continuing with the memory example described further above, if the chiparea of a memory at the present technology node is 60% bit area arrayand 40% support circuit area, then if chip architecture is not changed,and if bit area efficiency for a new technology node is improved by 2.8×while support circuit layout is improved by 2×, then bit area andsupport circuit areas will both be approximately 50% of chip area.Architecture changes and circuit design and layout improvements toincrease the number of bits per word and bit lines, such as global andlocal segmented word and bit lines described in U.S. Pat. No. 5,546,349,may be used to achieve 60% bit area and 40% support circuits for a new4× larger memory function chip design at a new technology node. However,the chip area will be 1.4× to 1.5× larger for the 4× the memoryfunction. So for example, if the present chip area is 100 mm², then thenew chip area for a 4× larger memory will be 140 to 150 mm²; if thepresent chip area is 70 mm², then the new chip area for a 4× largermemory function will be at least 100 mm².

From a fabrication (manufacturing) point of view, transition to highvolume production of a new 4× larger memory function at a new technologynode does not occur until the cost per bit of the new memory function iscompetitive with that of the present generation. Typically, at least twoand sometimes three new chips are designed with incremental reductionsin photolithographic linear dimensions (shrinks) of 10 to 15% each,reducing chip area of the 4× memory function to 100 mm² or less toincrease the number of chips per wafer and reduce the cost per bit ofmemory to levels competitive with the present generation memory.

Crafts et al., U.S. Pat. No. 5,536,968, the entire contents of which areincorporated herein by reference, discloses a OTP field-programmablememory having a cell formed by a diode in series with a nonvolatile OTPelement, in this patent a polysilicon fuse element. Each cell includesan as-formed polysilicon fuse of typically 100s of Ohms and a seriesselect diode. The memory array is a 2-D memory array with a long foldednarrow polyfuse element. If selected, milli-Amperes of current blow aselected polysilicon fuse which becomes nonconducting. The storage cellis large because of large polysilicon fuse dimensions, so the OTP memorydescribed in U.S. Pat. No. 5,536,968 does not address the memory scalingproblems describe further above.

Roesner, U.S. Pat. No. 4,442,507, the entire contents of which areincorporated herein by reference, discloses a one-time-programmable(OTP) field-programmable memory using a 3-dimensional (3-D) memory celland corresponding process, design, and architecture to replace the2-dimensional (2-D) memory approach of increasing chip area whilereducing individual component size (transistors) and interconnectionsfor each new generation of memory. U.S. Pat. No. 4,442,507 illustratesan EPROM (one-time-programmable) memory having a 3-D EPROM array inwhich cell select devices, storage devices, and interconnect means arenot fabricated in or on a semiconductor substrate, but are insteadformed on an insulating layer above support circuits formed in and on asemiconductor substrate with interconnections between support circuitsand the 3-D EPROM memory array. Such a 3-D memory approach significantlyreduces lithographic and process requirements associated with denserlarger memory function.

3-D EPROM prior art array 100 illustrated in FIG. 1 is a representationof a prior art corresponding structure in U.S. Pat. No. 4,442,507. Thememory cell includes a vertically-oriented Schottky diode in series withan antifuse formed above the Schottky diode using lightly dopedpolysilicon. Support circuits and interconnections 110 are formed in andon supporting semiconductor substrate 105, silicon for example.Interconnections through insulator 115 (not shown in FIG. 1) are used toconnect support circuits to array lines such as conductor 120 andconductor 170. Memory cells are fabricated on the surface of insulator115, include Schottky diode 142, antifuse 155, and interconnected bycombined conductor 120 and N+ polysilicon conductor 122, and metalconductor 170 and conductive barrier layer 160. Note that although thesurface of insulator 115 is illustrated as if planar, in fact it isnon-planar as illustrated in more detail in U.S. Pat. No. 4,442,507because VLSI planarization techniques were not available at the time ofthe invention.

N+ polysilicon patterned layer semiconductor 122 is used as one Schottkydiode 142 contact and as an array interconnect line. N+ polysiliconsemiconductor 122 may be silicon or germanium, for example, and istypically doped to 10²⁰ dopant atoms/cm³ with a resistance of 0.04Ohms/square. While semiconductor 122 may be used as an array line, alower resistance array line may be formed by depositing N+ polysiliconsemiconductor 122 on a molybdenum silicide conductor 120 between the N+semiconductor layer and the surface of insulator 115. A second N−polycrystalline silicon or germanium semiconductor patterned layer(semiconductor) 125, in contact with semiconductor 122, is typicallydoped in the range of 10¹⁴ to 10¹⁷ dopant atoms/cm³, with a resistanceof 15 Ohms/square and forms the cathode terminal of Schottky diode 142which is used as a cell selection device. Dopants may be arsenic,phosphorous, and antimony for example. Polysilicon conductors 122 and125 are typically 400 nm thick and 2 um in width.

The anode of Schottky diode device 142 is formed by patterned conductor140 using a noble metal such as platinum of thickness 25 nm deposited onN− polycrystalline silicon conductor 125, and heated to 600 degrees C.to form a compound (e.g. platinum silicide) with the underlyingpolycrystalline material. The silicide of noble metal 140 and theunderlying N-polysilicon semiconductor 125 forms junction 145 ofSchottky diode 142. Schottky diode 142 measurements resulted in aturn-on voltage of approximately 0.4 volts and a reverse breakdownvoltage of approximately 10 volts.

The nonvolatile state of the memory cell is stored in antifuse 155 as aresistive state. The resistive state of antifuse 155 is alterable(programmable) once (OTP) after the fabrication process is complete.Preferably, the material 150 used to form antifuse 155 is a singleelement N-semiconductor such as silicon or germanium, typically having adoping of less than 10¹⁷ atoms/cm³, where arsenic and phosphorous aresuitable N-type dopants as described further in U.S. Pat. No. 4,442,507.After patterning to form antifuse 155, a conductive barrier layer 160 ofTiW 100 nm thick is deposited in contact with antifuse 155 and insulator130. Then, an 800 nm aluminum layer is deposited and patterned to formconductor 170. Both conductor 170 and conductive barrier layer 160 arepatterned. Conductive barrier layer 160 is used to prevent aluminum frommigrating into the N-polysilicon material 150.

The resistance of the antifuse is typically 10⁷ ohms as formed.Initially, all antifuses in all cells have a resistance value ofapproximately 10⁷ ohms as-fabricated. If a cell is selected andprogrammed such that an antifuse threshold voltage of approximately 10volts is reached, then the antifuse resistance changes to 10² ohms, withprogramming current limited to approximately 50 uA, and with programmingtime in the microsecond range. An antifuse may be programmed only once,and the nonvolatile new lower resistance state stored in a memory cellof the 3-D EPROM memory with the array region above underlying supportcircuits 110 in and on semiconductor substrate 105.

While U.S. Pat. No. 4,442,507 introduces the concept of 3-D EPROM memoryarrays having all cell components and interconnections decoupled from asemiconductor substrate, and above support circuits, the approach islimited to OTP memories.

Prior art FIG. 2 illustrates a fabricated CMOS structure 200 and 200′including devices with a planar local interconnect metal layer and four(metal 1-metal 4) additional more-global planar stacked levels ofconductors, and stacked contacts and filled via holes (contact studs) asillustrated the prior art reference Ryan, J. G. et al., “The evolutionof interconnection technology at IBM”, Journal of Research andDevelopment, Vol. 39, No. 4, July 1995, pp. 371-381, the entire contentsof which are incorporated herein by reference. Metal 5 is nonplanar andis used to provide off-chip connections. Local interconnects and wiringlayers metal 1, metal 2, metal 3, metal 4, and metal 5 may use Al(Cu),W, Mo, Ti, Cu for example. Tight metal pitches require planarization forboth metals and oxides and near-vertical, zero overlap via studstypically formed using tungsten (W) as illustrated in FIG. 2. Extensiveuse of chemical-mechanical polishing (CMP) planarizing technology allowsformation of structures 200 and 200′. CMP technology is also illustratedin U.S. Pat. No. 4,944,836, the entire contents of which areincorporated herein by reference, issued Jul. 31, 1990. CMP technologyalso was chosen for its ability to remove prior level defects.

U.S. Pat. No. 5,670,803, the entire contents of which are incorporatedherein by reference, to co-inventor Bertin, discloses a 3-D SRAM arraystructure with simultaneously defined sidewall dimensions. Thisstructure includes vertical sidewalls simultaneously defined by trenchescutting through multiple layers of doped silicon and insulated regionsin order avoid (minimize) multiple alignment steps. These trenches cutthrough multiple semiconductor and oxide layers and stop on the topsurface of a supporting insulator (SiO₂) layer between the 3-D SRAMarray structure and an underlying semiconductor substrate. U.S. Pat. No.5,670,803 also teaches in-trench vertical local cell interconnect wiringwithin a trench region to form a vertically wired 3-D SRAM cell. U.S.Pat. No. 5,670,803 also teaches through-trench vertical interconnectwiring through a trench region to the top surface of a 3-D SRAM storagecell that has been locally wired within a trench cell.

SUMMARY

The present invention provides nonvolatile nanotube diodes andnonvolatile nanotube blocks and systems using same and methods of makingsame.

Under one aspect, a non-volatile nanotube diode device includes firstand second terminals; a semiconductor element including a cathode and ananode, and capable of forming a conductive pathway between the cathodeand anode in response to electrical stimulus applied to the firstconductive terminal; and a nanotube switching element including ananotube fabric article in electrical communication with thesemiconductive element, the nanotube fabric article disposed between andcapable of forming a conductive pathway between the semiconductorelement and the second terminal, wherein electrical stimuli on the firstand second terminals causes a plurality of logic states.

One or more embodiments include one or more of the following features.In a first logic state of the plurality of logic states a conductivepathway between the first and second terminals is substantially disabledand in a second logic state of the plurality of logic states aconductive pathway between the first and second terminals is enabled. Inthe first logic state the nanotube article has a relatively highresistance and in the second logic state the nanotube article has arelatively low resistance. The nanotube fabric article includes anon-woven network of unaligned nanotubes. In the second logic state thenon-woven network of unaligned nanotubes includes at least oneelectrically conductive pathway between the semiconductor element andthe second terminal. The nanotube fabric article is a multilayeredfabric. Above a threshold voltage between the first and secondterminals, the semiconductor element is capable of flowing current fromthe anode to the cathode and below the threshold voltage between thefirst and second terminals the semiconductor element is not capable offlowing current from the anode to the cathode. In the first logic state,the conductive pathway between the anode and the second terminal isdisabled. In the second logic state, the conductive pathway between theanode and the second terminal is enabled. A conductive contactinterposed between and providing an electrical communication pathwaybetween the nanotube fabric article and the semiconductor element. Thefirst terminal is in electrical communication with the anode and thecathode is in electrical communication with the conductive contact ofthe nanotube switching element. In the second logic state, the device iscapable of carrying electrical current substantially flowing from thefirst terminal to the second terminal. The first terminal is inelectrical communication with the cathode and the anode is in electricalcommunication with the conductive contact of the nanotube switchingelement. When in the second logic state, the device is capable ofcarrying electrical current substantially flowing from the secondterminal to the first terminal. The anode includes a conductive materialand the cathode includes an n-type semiconductor material. The anodeincludes a p-type semiconductor material and the cathode includes an-type semiconductor material.

Under another aspect, a two-terminal non-volatile state device includes:first and second terminals; a semiconductor field effect element havinga source, a drain, a gate in electrical communication with one of thesource and the drain, and a channel disposed between the source and thedrain, the gate capable of controllably forming an electricallyconductive pathway in the channel between the source and the drain; ananotube switching element having a nanotube fabric article and aconductive contact, the nanotube fabric article disposed between andcapable of forming an electrically conductive pathway between theconductive contact and the second terminal; wherein the first terminalis in electrical communication with one of the source and the drain, theother of the source and drain is in electrical communication with theconductive contact; and wherein a first set of electrical stimuli on thefirst and second conductive terminals causes a first logic state and asecond set of electrical stimuli on the first and second conductiveterminals causes a second logic state.

One or more embodiments include one or more of the following features.The first logic state corresponds to a relatively non-conductive pathwaybetween the first and second terminals and the second logic statecorresponds to a conductive pathway between the first and secondterminals. The first set of electrical stimuli causes a relatively highresistance state in the nanotube fabric article and the second set ofelectrical stimuli causes a relatively low resistance state in thenanotube fabric article. The nanotube fabric article includes anon-woven network of unaligned nanotubes. The nanotube fabric articleincludes a multilayered fabric. In response to the second set ofelectrical stimuli, the non-woven network of unaligned nanotubesprovides at least one electrically conductive pathway between theconductive contact and the semiconductor field-effect element. Inresponse to the second set of electrical stimuli, a conductive pathwaybetween the source and the drain is formed in the conductive channel.The semiconductor field effect element includes a PFET. Thesemiconductor field effect element includes a NFET. The source of thesemiconductor field-effect element is in electrical communication withthe first terminal and the drain is in electrical communication with theconductive contact of the nanotube switching element. The drain of thesemiconductor field-effect element is in electrical communication withthe first terminal and the source of the is in electrical communicationwith the conductive contact of the nanotube switching element.

Under another aspect, a voltage selection circuit includes: an inputvoltage source; an output voltage terminal and a reference voltageterminal; a resistive element; and a nonvolatile nanotube diode deviceincluding: first and second terminals; a semiconductor element inelectrical communication with the first terminal; a nanotube switchingelement disposed between and capable of conducting electrical stimulusbetween the semiconductor element and the second terminal; wherein thenonvolatile nanotube diode device is capable of conducting electricalstimulus between the first and second terminals, wherein the resistiveelement is disposed between the input voltage source and the outputvoltage terminal, the nonvolatile nanotube diode device is disposedbetween and in electrical communication with the output voltage terminaland the reference voltage terminal, and wherein the voltage selectioncircuit is capable of providing a first output voltage level when, inresponse to electrical stimulus at the input voltage source and thereference voltage terminal, the nonvolatile nanotube diode substantiallyprevents the conduction of electrical stimulus between the first andsecond terminals and wherein the voltage selection circuit is capable ofproviding a second output voltage level when, in response to electricalstimulus at the input voltage source and the reference voltage terminal,the nonvolatile nanotube diode conducts electrical stimulus between thefirst and second terminals.

One or more embodiments include one or more of the following features.The semiconductor element includes an anode and a cathode, the anode inelectrical communication with the first terminal and the cathode incommunication with the nanotube switching element. The semiconductorelement includes a field effect element having a source region incommunication with the first terminal, a drain region in electricalcommunication with the nanotube switching element, a gate region inelectrical communication with one of the source region and the drainregion, and a channel region capable of controllably forming andunforming an electrically conductive pathway between the source and thedrain in response to electrical stimulus on the gate region. The firstoutput voltage level is substantially equivalent to the input voltagesource. The second output voltage level is substantially equivalent tothe reference voltage terminal. The nanotube switching element includesa nanotube fabric article capable of a high resistance state and a lowresistance state. The high resistance state of the nanotube fabricarticle is substantially higher than the resistance of the resistiveelement and wherein the low resistance state of the nanotube fabricarticle is substantially lower than the resistance of the resistiveelement. The first output voltage level is determined, in part, by therelative resistance of the resistive element and the high resistancestate of the nanotube fabric article, and wherein the second outputvoltage level is determined, in part, by the relative resistance of theresistive element and the low resistance state of the nanotube fabricarticle.

Under another aspect, a nonvolatile nanotube diode includes a substrate;a semiconductor element disposed over the substrate, the semiconductorelement having an anode and a cathode and capable of forming anelectrically conductive pathway between the anode and the cathode; ananotube switching element disposed over the semiconductor element, thenanotube switching element including a conductive contact and a nanotubefabric element capable of a plurality of resistance states; and aconductive terminal disposed in spaced relation to the conductivecontact, wherein the nanotube fabric element is interposed between andin electrical communication with the conductive contact and theconductive contact is in electrical communication with the cathode, andwherein in response to electrical stimuli applied to the anode and theconductive terminal, the nonvolatile nanotube diode is capable offorming an electrically conductive pathway between the anode and theconductive terminal.

One or more embodiments include one or more of the following features.The anode includes a conductor material and the cathode includes asemiconductor material. The anode material includes at least one of Al,Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo Na, Ni, Os, Pb, Pd, Pt, Rb, Ru,Ti, W, Zn, CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂ and ZrSi₂. Thesemiconductor element includes a Schottky barrier diode. A secondconductive terminal interposed between the substrate and the anode, thesecond conductive terminal in electrical communication with the anode,wherein in response to electrical stimuli at said second conductiveterminal and the conductive terminal, the nonvolatile nanotube diode iscapable of forming an electrically conductive pathway between saidsecond conductive terminal and the conductive terminal. The anodeincludes a semiconductor material of a first type and the cathode regionincludes a semiconductor material of a second type. The semiconductormaterial of the first type is positively doped, the semiconductormaterial of the second type is negatively doped, and the semiconductorelement forms a PN junction. The nanotube fabric element issubstantially vertically disposed. The nanotube fabric element issubstantially horizontally disposed. The nanotube fabric elementincludes a nonwoven multilayered fabric. The nanotube fabric element hasa thickness between approximately 20 nm and approximately 200 nm. Theconductive contact is disposed substantially coplanar to a lower surfaceof the nanotube fabric element and the conductive terminal is disposedsubstantially coplanar to an upper surface of the nanotube fabricelement. The semiconductor element is a field effect transistor.

Under another aspect, a nonvolatile nanotube diode includes a substrate;a conductive terminal disposed over the substrate; a semiconductorelement disposed over the conductive terminal, the semiconductor elementhaving a cathode and an anode and capable of forming an electricallyconductive pathway between the cathode and the anode; and a nanotubeswitching element disposed over the semiconductor element, the nanotubeswitching element including a conductive contact and nanotube fabricelement capable of a plurality of resistance states, wherein thenanotube fabric element is interposed between and in electricalcommunication with anode and the conductive contact and cathode is inelectrical communication with the conductive terminal, and wherein inresponse to electrical stimuli applied to the anode and the conductiveterminal, the nonvolatile nanotube diode is capable of forming anelectrically conductive pathway between the conductive terminal and theconductive contact.

One or more embodiments include one or more of the following features.The anode includes a conductor material and the cathode includes asemiconductor material. The anode material includes at least one of Al,Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo Na, Ni, Os, Pb, Pd, Pt, Rb, Ru,Ti, W, Zn, CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂ and ZrSi₂. Thesemiconductor element includes a Schottky barrier diode. A secondconductive terminal interposed between and providing an electricallyconductive path between the anode and the patterned region of nonwovennanotube fabric. The anode includes a semiconductor material of a firsttype and the cathode region includes a semiconductor material of asecond type. The semiconductor material of the first type is positivelydoped, the semiconductor material of the second type is negativelydoped, and the semiconductor element forms a PN junction. The nanotubefabric element is substantially vertically disposed. The nanotube fabricelement is substantially horizontally disposed. The nanotube fabricelement includes a layer of nonwoven nanotubes having a thicknessbetween approximately 0.5 and approximately 20 nanometers. The nanotubefabric element includes a nonwoven multilayered fabric. The conductivecontact is disposed substantially coplanar to a lower surface of thenanotube fabric element and the conductive terminal is disposedsubstantially coplanar to an upper surface of the nanotube fabricelement. The semiconductor element includes a field effect transistor.

Under another aspect, a memory array includes a plurality of word lines;a plurality of bit lines; a plurality of memory cells, each memory cellresponsive to electrical stimulus on a word line and on a bit line, eachmemory cell including: a two-terminal non-volatile nanotube switchingdevice including a first and a second terminal, a semiconductor diodeelement, and a nanotube fabric article, the semiconductor diode and ananotube article disposed between and in electrical communication withthe first and second terminals, wherein the nanotube fabric article iscapable of a plurality of resistance states, and wherein the firstterminal is coupled to the one word line and the second terminal iscoupled to the one bit line, the electrical stimulus applied to thefirst and second terminals capable of changing the resistance state ofthe nanotube fabric article; and a memory operation circuit operablycoupled to each bit line of the plurality of bit lines and each wordline of the plurality of word lines, said operation circuit capable ofselecting each of the cells by activating at least one of the bit lineand the word line coupled to that cell to apply a selected electricalstimulus to each of the corresponding first and second terminals, andsaid operation circuit further capable of detecting a resistance stateof the nanotube fabric article of a selected memory cell and adjustingthe electrical stimulus applied to each of the corresponding first andsecond terminals in response to the resistance state to controllablyinduce a selected resistance state in the nanotube fabric article,wherein the selected resistance state of the nanotube fabric article ofeach memory cell corresponds to an informational state of said memorycell.

One or more embodiments include one or more of the following features.Each memory cell nonvolatily stores the corresponding information statein response to electrical stimulus applied to each of the correspondingfirst and second terminals. The semiconductor diode element includes acathode and an anode, the anode in electrical communication with thesecond terminal and the cathode in electrical communication with thenanotube switching element. The cathode includes a first semiconductormaterial and the anode includes a second semiconductor material. Thesemiconductor diode element includes a cathode and an anode, the cathodein electrical communication with the first terminal and the anode inelectrical communication with the nanotube switching element. Thecathode includes a first semiconductor material and the anode includes asecond semiconductor material. The cathode includes a semiconductormaterial and the anode includes a conductive material and forms aconductive contact to the nanotube fabric article. A conductive contactinterposed between the semiconductor diode element and the nanotubefabric article. The nanotube fabric article includes a network ofunaligned nanotubes capable of providing at least one electricallyconductive pathway between the first conductive contact and one of thefirst and second terminals. The nanotube fabric article includes amultilayered nanotube fabric. The multilayered nanotube article has athickness that defines a spacing between the conductive contact and oneof the first and second conductive terminals. The plurality of memorycells includes multiple pairs of stacked memory cells, wherein a firstmemory cell in each pair of stacked memory cells is disposed above andin electrical communication with a first bit line and the word line isdisposed above and in electrical communication with the first memorycell; and wherein a second memory cell in each pair of stacked memorycells is disposed above and in electrical communication with the wordline and a second bit line is disposed above and in electricalcommunication with the second memory cell. The resistance state of thenanotube article in the first memory cell is substantially unaffected bythe resistance state of the nanotube article in the second memory celland the resistance state of the nanotube article in the second memorycell is substantially unaffected by the resistance state of the nanotubearticle in the first memory cell. The resistance state of the nanotubearticle in the first memory cell is substantially unaffected by saidoperation circuit selecting the second memory cell and the resistancestate of the nanotube article in the second memory cell is substantiallyunaffected by the resistance state by said operation circuit selectingthe first memory cell. The resistance state of the nanotube article inthe first memory cell is substantially unaffected by said operationcircuit detecting a resistance state of the nanotube fabric article ofthe second memory cell and the resistance state of the nanotube articlein the second memory cell is substantially unaffected by the resistancestate by said operation circuit detecting a resistance state of thenanotube fabric article of the first memory cell. The resistance stateof the nanotube article in the first memory cell is substantiallyunaffected by said operation circuit adjusting the electrical stimulusapplied to each of the corresponding first and second terminals of thesecond memory cell and the resistance state of the nanotube article inthe second memory cell is substantially unaffected by the resistancestate by said operation circuit adjusting the electrical stimulusapplied to each of the corresponding first and second terminals of thefirst memory cell. An insulating region and a plurality of conductiveinterconnects wherein the insulating region is disposed over the memoryoperation circuit, the plurality of memory cells are disposed over theinsulating region, and the plurality of conductive interconnectsoperably couple the memory operation circuit to the plurality of bitlines and plurality of word lines. Adjusting the electrical stimulusincludes incrementally changing the voltage applied to each of thecorresponding first and second terminals. Incrementally changing thevoltage includes applying voltage pulses. Amplitudes of subsequentvoltage pulses are incrementally increased by approximately 200 mV.Adjusting the electrical stimulus includes changing the current suppliedto at least one of the corresponding first and second terminals.Substantially removing electrical stimulus from the corresponding bitline and word line after controllably inducing the selected resistancestate in the nanotube fabric article to substantially preserve theselected resistance state of the nanotube fabric article. Detecting theresistance state of the nanotube fabric article further includesdetecting a variation over time of electrical stimulus on acorresponding bit line. Detecting the resistance state of the nanotubefabric article further includes detecting a current flow though acorresponding bit line. In each two terminal nonvolatile nanotubeswitching device, current is capable of flowing from the second terminalto the first terminal and substantially prevented from flowing from thefirst terminal to the second terminal. Current is capable of flowingfrom the second terminal to the first terminal when a threshold voltageis reached by applying electrical stimulus to each of the correspondingfirst and second terminals. The selected resistance state of thenanotube fabric article of each memory cell includes one of a relativelyhigh resistance state corresponding to a first informational state ofsaid memory cell and a relatively low resistance state corresponding toa second informational state of said memory cell. A third informationstate of each memory cell corresponds to a state in which current iscapable of flowing from the second terminal to the first terminal andwherein a fourth information state of each memory cell corresponds to astate in which current is substantially prevented from flowing from thefirst terminal to the second terminal. The two-terminal non-volatilenanotube switching device is operable independently of the voltagepolarity between the first and second terminals. The two-terminalnon-volatile nanotube switching device is operable independently of thedirection of current flow between the first and second terminals. Theplurality of memory cells includes multiple pairs of stacked memorycells, wherein a first memory cell in each pair of stacked memory cellsis disposed above and in electrical communication with a first bit lineand the word line is disposed above and in electrical communication withthe first memory cell; wherein an insulator material is disposed overthe first memory cell; wherein a second memory cell in each pair ofstacked memory cells is disposed above and in electrical communicationwith a second word line, the second word line disposed over theinsulator material and wherein a second bit line is disposed above andin electrical communication with the second memory cell. The pluralityof memory cells includes multiple pairs of stacked memory cells, whereina first memory cell in each pair of stacked memory cells is disposedabove and in electrical communication with a first bit line and the wordline is disposed above and in electrical communication with the firstmemory cell; wherein an insulator material is disposed over the firstmemory cell; wherein a second memory cell in each pair of stacked memorycells is disposed above and in electrical communication with a secondbit line, the second bit line disposed over the insulator material andwherein a second word line is disposed above and in electricalcommunication with the second memory cell.

Under another aspect, a method of making a nanotube switch includes:providing a substrate having a first conductive terminal; depositing amultilayer nanotube fabric over the first conductive terminal; anddepositing a second conductive terminal over the multilayer nanotubefabric, the nanotube fabric having a thickness, density, and compositionselected to prevent direct physical and electrical contact between thefirst and second conductive terminals.

One or more embodiments include one or more of the following features.Lithographically patterning the first and second conductive terminalsand the multilayer nanotube fabric so as to each have substantially thesame lateral dimensions. The first and second conductive terminals andthe multilayer nanotube fabric each have a substantially circularlateral shape. The first and second conductive terminals and themultilayer nanotube fabric each have a substantially rectangular lateralshape. The first and second conductive terminals and the multilayernanotube fabric each have lateral dimensions of between about 200 nm×200nm and about 22 nm×22 nm. The first and second conductive terminals andthe multilayer nanotube fabric each have a lateral dimension of betweenabout 22 nm and about 10 nm. The first and second conductive terminalsand the multilayer nanotube fabric each have a lateral dimension of lessthan 10 nm. The multilayer nanotube fabric has a thickness between about10 nm and about 200 nm. The multilayer nanotube fabric has a thicknessbetween about 10 nm and about 50 nm. The substrate includes a diodeunder the first conductive terminal, the diode being addressable bycontrol circuitry. Lithographically patterning the first and secondconductive terminals, the multilayer nanotube fabric, and the diode soas to each have substantially the same lateral dimensions. Providing asecond diode over the second conductive terminal, depositing a thirdconductive terminal over the second diode, depositing a secondmultilayer nanotube fabric over the third conductive terminal, anddepositing a fourth conductive terminal over the second multilayernanotube fabric. Lithographically patterning the multilayer nanotubefabrics, the diodes, and the conductive terminals so as to each havesubstantially the same lateral dimensions. The diode includes a layer ofN+ polysilicon, a layer of N polysilicon, and a layer of conductor. Thediode includes a layer of N+ polysilicon, a layer of N polysilicon, anda layer of P polysilicon. Providing a diode over the second conductiveterminal, the diode being addressable by control circuitry. Annealingthe diode at a temperature exceeding 700° C. Lithographically patterningthe first and second conductive terminals, the multilayer nanotubefabric, and the diode so as to each have substantially the same lateraldimensions. The substrate includes a semiconductor field effecttransistor, at least a portion of which is under the first conductiveterminal, the semiconductor field effect transistor being addressable bycontrol circuitry. Depositing the multilayer nanotube fabric includesspraying nanotubes dispersed in a solvent onto the first conductiveterminal. Depositing the multilayer nanotube fabric includes spincoating nanotubes dispersed in a solvent onto the first conductiveterminal. Depositing the multilayer nanotube fabric includes depositinga mixture of nanotubes and a matrix material dispersed in a solvent ontothe first conductive terminal. Removing the matrix material afterdepositing the second conductive terminal. The matrix material includespolypropylene carbonate. The first and second conductive terminals eachinclude a conductive material independently selected from the groupconsisting of Ru, Ti, Cr, Al, Al(Cu), Au, Pd, Pt, Ni, Ta, W, Cu, Mo, Ag,In, Ir, Pb, Sn, TiAu, TiCu, TiPd, PbIn, TiW, RuN, RuO, TiN, TaN,CoSi_(x), and TiSi_(x). Depositing a porous dielectric material on themultilayer nanotube fabric. The porous dielectric material includes oneof a spin-on glass and a spin-on low-K dielectric. Depositing anonporous dielectric material on the multilayer nanotube fabric. Thenonporous dielectric material includes a high-K dielectric. Thenonporous dielectric material includes hafnium oxide. Providing a wordline in electrical communication with the second conductive terminal.

Under another aspect, a method of making a nanotube diode includes:providing a substrate having a first conductive terminal; depositing amultilayer nanotube fabric over the first conductive terminal;depositing a second conductive terminal over the multilayer nanotubefabric, the nanotube fabric having a thickness, density, and compositionselected to prevent direct physical and electrical contact between thefirst and second conductive terminals; and providing a diode inelectrical contact with one of the first and second conductiveterminals.

One or more embodiments include one or more of the following features.Providing the diode after depositing the multilayer nanotube fabric.Annealing the diode at a temperature exceeding 700° C. Positioning thediode over and in electrical contact with the second conductiveterminal. Positioning the diode under and in electrical contact with thefirst conductive terminal. Lithographically patterning the first andsecond conductive terminals, the multilayer nanotube fabric, and thediode so as to each have substantially the same lateral dimensions. Thefirst and second conductive terminals, the multilayer nanotube fabric,and the diode each have a substantially circular lateral shape. Thefirst and second conductive terminals, the multilayer nanotube fabric,and the diode each have a substantially rectangular lateral shape. Thefirst and second conductive terminals and the multilayer nanotube fabriceach have lateral dimensions of between about 200 nm×200 nm and about 22nm×22 nm.

Under another aspect, a non-volatile nanotube switch includes a firstconductive terminal; a nanotube block including a multilayer nanotubefabric, at least a portion of the nanotube block being positioned overand in contact with at least a portion of the first conductive terminal;a second conductive terminal, at least a portion of the secondconductive terminal being positioned over and in contact with at least aportion of the nanotube block, wherein the nanotube block is constructedand arranged to prevent direct physical and electrical contact betweenthe first and second conductive terminals; and control circuitry inelectrical communication with and capable of applying electricalstimulus to the first and second conductive terminals, wherein thenanotube block is capable of switching between a plurality of electronicstates in response to a corresponding plurality of electrical stimuliapplied by the control circuitry to the first and second conductiveterminals, and wherein, for each different electronic state of theplurality of electronic states, the nanotube block provides anelectrical pathway of corresponding different resistance between thefirst and second conductive terminals.

One or more embodiments include one or more of the following features.Substantially the entire nanotube block is positioned over substantiallythe entire first conductive terminal, and wherein substantially theentire second conductive terminal is positioned over substantially theentire nanotube block. The first and second conductive terminals and thenanotube block each have a substantially circular lateral shape. Thefirst and second conductive terminals and the nanotube block each have asubstantially rectangular lateral shape. The first and second conductiveterminals and the nanotube block each have a lateral dimension betweenabout 200 nm and about 22 nm. The first and second conductive terminalsand the nanotube block each have a lateral dimension between about 22 nmand about 10 nm. The first and second conductive terminals and thenanotube block each have lateral dimension of less than about 10 nm. Thenanotube block has a thickness between about 10 nm and about 200 nm. Thenanotube block has a thickness between about 10 nm and about 50 nm. Thecontrol circuitry includes a diode in direct physical contact with thefirst conductive terminal. The first conductive terminal is positionedover the diode. The diode is positioned over the second conductiveterminal. The diode, the nanotube block, and the first and secondconductive terminals have substantially the same lateral dimensions. Thediode includes a layer of N+ polysilicon, a layer of N polysilicon, anda layer of conductor. The diode includes a layer of N+ polysilicon, alayer of N polysilicon, and a layer of P polysilicon. The controlcircuitry includes a semiconductor field effect transistor in contactwith the first conductive terminal. The first and second conductiveterminals each include a conductive material independently selected fromthe group consisting of Ru, Ti, Cr, Al, Al(Cu), Au, Pd, Pt, Ni, Ta, W,Cu, Mo, Ag, In, Ir, Pb, Sn, TiAu, TiCu, TiPd, PbIn, TiW, RuN, RuO, TiN,TaN, CoSi_(x), and TiSi_(x). The nanotube block further includes aporous dielectric material. The porous dielectric material includes oneof a spin-on glass and a spin-on low-K dielectric. The nanotube blockfurther includes a nonporous dielectric material. The nonporousdielectric material includes hafnium oxide.

Under another aspect, a high-density memory array includes: a pluralityof word lines and a plurality of bit lines; a plurality of memory cells,each memory cell including: a first conductive terminal; a nanotubeblock over the first conductive terminal, the nanotube block including amultilayer nanotube fabric; a second conductive terminal over thenanotube block and in electrical communication with a word line of theplurality of word lines; and a diode in electrical communication with abit line of the plurality of bit lines and one of the first and secondconductive terminals, wherein the nanotube block has a thickness thatdefines a spacing between the first and second conductive terminals, andwherein a logical state of each memory cell is selectable by activationonly of the bit line and the word line connected to that memory cell.The diode is positioned under the first conductive terminal. The diodeis positioned over the second conductive terminal. The diode, the firstand second conductive terminals, and the nanotube block all havesubstantially the same lateral dimensions. The diode, the first andsecond conductive terminals, and the nanotube block each have asubstantially circular lateral shape. The diode, the first and secondconductive terminals, and the nanotube block each have a substantiallyrectangular lateral shape. The diode, the first and second conductiveterminals, and the nanotube block each have a lateral dimension betweenabout 200 nm and about 22 nm. The memory cells are spaced from eachother by between about 200 nm and about 22 nm. The first and secondconductive terminals, and the nanotube block each have a lateraldimension between about 22 nm and about 10 nm. The memory cells of thearray are spaced from each other by between about 220 nm and about 10nm. Some memory cells of the array are laterally spaced relative to eachother, and other memory cells of the array are stacked on top of eachother. Some of the memory cells of the array that are stacked on top ofeach other share a bit line. Some of the memory cells of the array thatare laterally spaced relative to each other share a word line. Theplurality of word lines are substantially perpendicular to the pluralityof bit lines. The thickness of the nanotube block is between about 10 nmand about 200 nm. The thickness of the nanotube block is between about10 nm and about 50 nm.

Under another aspect, a high-density memory array includes: a pluralityof word lines and a plurality of bit lines; a plurality of memory cells,each memory cell including: a first conductive terminal; a nanotubeblock over the first conductive terminal, the nanotube block including amultilayer nanotube fabric; a second conductive terminal over thenanotube block and in electrical communication with a bit line of theplurality of bit lines; and a diode in electrical communication with aword line of the plurality of word lines, wherein the nanotube block hasa thickness that defines a spacing between the first and secondconductive terminals, wherein a logical state of each memory cell isselectable by activation only of the bit line and the word lineconnected to that memory cell. The diode is positioned under the firstconductive terminal. The diode is positioned over the second conductiveterminal. The diode, the first and second conductive terminals, and thenanotube block all have substantially the same lateral dimensions. Thediode, the first and second conductive terminals, and the nanotube blockeach have a substantially circular lateral shape. The diode, the firstand second conductive terminals, and the nanotube block each have asubstantially rectangular lateral shape. The diode, the first and secondconductive terminals, and the nanotube block each have a lateraldimension between about 200 nm and about 22 nm. The memory cells arespaced from each other by between about 200 nm and about 22 nm. Thediode, the first and second conductive terminals, and the nanotube blockeach have a lateral dimension between about 22 nm and about 10 nm. Thememory cells of the array are spaced from each other by between about220 nm and about 10 nm. Some memory cells of the array are laterallyspaced relative to each other, and other memory cells of the array arestacked on top of each other. Some of the memory cells of the array thatare stacked on top of each other share a bit line. Some of the memorycell of the array that are laterally spaced relative to each other sharea word line. The plurality of word lines are substantially perpendicularto the plurality of bit lines. The thickness of the nanotube block isbetween about 10 nm and about 200 nm. The thickness of the nanotubeblock is between about 10 nm and about 50 nm.

Under another aspect, a high-density memory array includes: a pluralityof word lines and a plurality of bit lines; a plurality of memory cellpairs, each memory cell pair including: a first memory cell including afirst conductive terminal, a first nanotube element over the firstconductive terminal, a second conductive terminal over the nanotubeelement, and a first diode in electrical communication with one of thefirst and second conductive terminals and with a first bit line of theplurality of bit lines; and a second memory cell including a thirdconductive terminal, a second nanotube element over the first conductiveterminal, a fourth conductive terminal over the nanotube element, and asecond diode in electrical communication with one of the third andfourth conductive terminals and with a second bit line of the pluralityof bit lines, wherein the second memory cell is positioned over thefirst memory cell, and wherein the first and second memory cell share aword line of the plurality of word lines; wherein each memory cell pairof the plurality of memory cells is capable of switching between atleast four different resistance states corresponding to four differentlogic states in response to electrical stimuli at the first and secondbit lines and the shared word line.

Under another aspect, a high-density memory array includes: a pluralityof word lines and a plurality of bit lines; a plurality of memory cellpairs, each memory cell pair including: a first memory cell including afirst conductive terminal, a first nanotube element over the firstconductive terminal, a second conductive terminal over the nanotubeelement, and a first diode in electrical communication with one of thefirst and second conductive terminals and with a first word line of theplurality of word lines; and a second memory cell including a thirdconductive terminal, a second nanotube element over the first conductiveterminal, a fourth conductive terminal over the nanotube element, and asecond diode in electrical communication with one of the third andfourth conductive terminals and with a second word line of the pluralityof word lines, wherein the second memory cell is positioned over thefirst memory cell, and wherein the first and second memory cell share abit line of the plurality of bit lines; wherein each memory cell pair ofthe plurality of memory cells is capable of switching between at leastfour different resistance states corresponding to four different logicstates in response to electrical stimuli at the first and second wordlines and the shared bit line.

Under another aspect, a nanotube diode includes: a cathode formed of asemiconductor material; and an anode formed of nanotubes, wherein thecathode and the anode are in fixed and direct physical contact; andwherein the cathode and anode are constructed and arranged such thatsufficient electrical stimulus applied to the cathode and the anodecreates a conductive pathway between the cathode and the anode.

One or more embodiments include one or more of the following features.The anode includes a non-woven nanotube fabric having a plurality ofunaligned nanotubes. The non-woven nanotube fabric includes a layer ofnanotubes having a thickness between approximately 0.5 and approximately20 nanometers. The non-woven nanotube fabric includes a block ofnanotubes. The nanotubes include metallic nanotubes and semiconductingnanotubes. The cathode includes an n-type semiconductor material. ASchottky barrier is formed between the n-type semiconductor material andthe metallic nanotubes. A PN junction is formed between the n-typesemiconductor material and the semiconducting nanotubes. A PN junctionis formed between the n-type semiconductor material and thesemiconducting nanotubes. The Schottky barrier and the PN junctionprovide electrically parallel communication pathways between the cathodeand the anode. Further in electrical communication with a nonvolatilememory cell, the nanotube diode capable of controlling electricalstimulus to the nonvolatile memory cell. Further in electricalcommunication with a nonvolatile nanotube switch, the nanotube diodecapable of controlling electrical stimulus to the nonvolatile nanotubeswitch. Further in electrical communication with an electrical networkof switching elements, the nanotube diode capable of controllingelectrical stimulus to the electrical network of switching elements.Further in communication with a storage element, the nanotube diodecapable of selecting the storage element in response to electricalstimulus. The storage element is nonvolatile. Further in communicationwith an integrated circuit, the nanotube diode operable as a rectifierfor the integrated circuit.

Under another aspect, a nanotube diode includes: a conductive terminal;a semiconductor element disposed over and in electrical communicationwith the conductive terminal, wherein the semiconductor element forms acathode; and a nanotube switching element disposed over and in fixedelectrical communication with the semiconductor element, wherein thenanotube switching element forms an anode, wherein the nanotubeswitching element includes a conductive contact and nanotube fabricelement capable of a plurality of resistance states, and wherein thecathode and the anode are constructed and arranged such that in responseto sufficient electrical stimuli applied to the conductive contact andthe conductive terminal, the nonvolatile nanotube diode is capable offorming an electrically conductive pathway between the conductiveterminal and the conductive contact.

One or more embodiments include one or more of the following features.The nanotube fabric element includes a patterned region of nanotubes andthe semiconductor element includes an n-type semiconductor material. Thepatterned region of nanotubes includes metallic nanotubes andsemiconducting nanotubes. A Schottky barrier is formed between then-type semiconductor material and the metallic nanotubes including thepatterned region of nanotubes. A PN junction is formed between then-type semiconductor material and the semiconducting nanotubes includingthe patterned region of nanotubes. The Schottky barrier and the PNjunction provide electrically parallel communication pathways betweenthe conducting terminal and the nanotube fabric element. Further inelectrical communication with a nonvolatile memory cell, the nanotubediode capable of controlling electrical stimulus to the nonvolatilememory cell. Further in electrical communication with a nonvolatilenanotube switch, the nanotube diode capable of controlling electricalstimulus to the nonvolatile nanotube switch. Further in electricalcommunication with an electrical network of switching elements, thenanotube diode capable of controlling electrical stimulus to theelectrical network of switching elements. Further in communication witha storage element, the nanotube diode capable of selecting the storageelement in response to electrical stimulus. The storage element isnonvolatile. Further in communication with an integrated circuit, thenanotube diode operable as a rectifier for the integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawing:

FIG. 1 illustrates a prior art adaptation of a 3D-EPROM cell in whichthe array is on an insulating layer above memory support circuits formedin and on an underlying semiconductor substrate.

FIG. 2 illustrates prior art CMOS structure with planarized wiring andstacked vertical vias.

FIG. 3 illustrates an embodiment of a nonvolatile nanotube switch in anessentially horizontal orientation in which two terminals are deposited,each one at opposite ends of a patterned nanotube channel element.

FIG. 4 illustrates an embodiment of a nonvolatile nanotube switch in anessentially horizontal orientation in which a conformal nanotube channelelement is deposited on predefined terminal regions.

FIG. 5 illustrates an embodiment of a nonvolatile nanotube switch inwhich a nanotube channel element is deposited in an essentiallyhorizontal orientation on predefined terminal regions that includes acoplanar insulator region between the terminals.

FIGS. 6A-6B illustrate an SEM views of embodiments of nonvolatilenanotube switches similar to the embodiment of a nonvolatile nanotubeswitch illustrated in FIG. 3 in an ON conducting state and in an OFFnon-conducting state.

FIG. 7A illustrates an embodiment of a conformal nanofabric layer havingan essentially vertical orientation over a stepped region.

FIG. 7B is an embodiment of a representation of a 3-D memory cell crosssection with a vertically-oriented nonvolatile nanotube switch storageelement.

FIG. 8 illustrates a schematic representation of an embodiment of anonvolatile nanotube switch.

FIGS. 9A-9B illustrate ON and OFF resistance values for exemplarynanotube channel element channel lengths of 250 nm and 22 nm.

FIG. 10 illustrates nonvolatile nanotube switch erase voltage as afunction of nonvolatile nanotube channel length for a plurality ofexemplary nanotube switches.

FIGS. 11A-11B illustrate nonvolatile nanotube switch voltage and currentoperational waveforms for erase, program, and read operating modes foran exemplary nanotube switch.

FIG. 12 illustrates a schematic diagram of an embodiment of a twoterminal nonvolatile nanotube diode formed by a diode and a nonvolatilenanotube switch in series, with a cathode-to-nanotube electricalconnection.

FIG. 13 illustrates a schematic diagram of an embodiment of a twoterminal nonvolatile nanotube diode formed by a diode and a nonvolatilenanotube switch in series, with an anode-to-nanotube electricalconnection.

FIGS. 14 and 15 illustrate schematic diagrams of embodiments of twoterminal nonvolatile nanotube diodes formed by NFET-diodes and anonvolatile nanotube switches in series.

FIGS. 16 and 17 illustrate schematic diagrams of embodiments of twoterminal nonvolatile nanotube diodes formed by PFET-diodes and anonvolatile nanotube switches in series.

FIG. 18 illustrates an embodiment having the nonvolatile nanotube diodeof FIG. 12 and two stimulus sources.

FIG. 19 illustrates an embodiment having the nonvolatile nanotube diodeof FIG. 15 and two stimulus sources.

FIGS. 20A-20B illustrates mode setting waveforms for changing thenonvolatile state of nonvolatile nanotube diodes, according to someembodiments.

FIGS. 21A-21E illustrate a circuit and device electrical characteristicsof nonvolatile nanotube diodes similar to the nonvolatile nanotube diodeillustrated in FIG. 12, according to some embodiments.

FIG. 22 illustrates circuit operating waveforms of the circuit shown inFIG. 21A, according to some embodiments.

FIG. 23A illustrates an embodiment of a circuit using nonvolatilenanotube diodes similar to the nonvolatile nanotube diode illustrated inFIG. 15.

FIG. 23B illustrates circuit operating waveforms of the circuit shown inFIG. 23A, according to some embodiments.

FIG. 24 illustrates an embodiment of a transfer circuit using anonvolatile nanotube diode corresponding to the nonvolatile nanotubediode of FIG. 12.

FIG. 25 illustrates the circuit operating waveforms of the circuit shownin FIG. 24, according to some embodiments.

FIG. 26A schematically illustrates an embodiment of a memory schematicthat uses nonvolatile nanotube diodes illustrated in FIG. 12 asnonvolatile memory cells.

FIG. 26B illustrates operational waveforms for the memory illustrated inFIG. 26A, according to some embodiments.

FIGS. 27A-27B illustrate methods of fabrication of memory cells usingnonvolatile nanotube diodes similar to those illustrated schematicallyin FIG. 12, according to some embodiments.

FIG. 28A illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with a cathode-to-nanotubenonvolatile nanotube diode with a Schottky diode in series with avertically oriented nonvolatile nanotube switch within vertical cellboundaries.

FIG. 28B illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with a cathode-to-nanotubenonvolatile nanotube diode with a PN diode in series with a verticallyoriented nonvolatile nanotube switch within vertical cell boundaries.

FIG. 28C illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with a cathode-to-nanotubenonvolatile nanotube diode with a Schottky diode in series with ahorizontally oriented nonvolatile nanotube switch within vertical cellboundaries.

FIG. 29A schematically illustrates an embodiment of a memory schematicthat uses nonvolatile nanotube diodes illustrated in FIG. 13 asnonvolatile memory cells.

FIG. 29B illustrates operational waveforms for the memory illustrated inFIG. 29A, according to some embodiments.

FIGS. 30A-30B illustrate methods of fabrication of memory cells usingnonvolatile nanotube diodes similar to those illustrated schematicallyin FIG. 13, according to some embodiments;

FIG. 31A illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with an anode-to-nanotubenonvolatile nanotube diode with a Schottky diode in series with avertically oriented nonvolatile nanotube switch within vertical cellboundaries.

FIG. 31B illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with an anode-to-nanotubenonvolatile nanotube diode with a PN diode in series with a verticallyoriented nonvolatile nanotube switch within vertical cell boundaries.

FIG. 31C illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with an anode-to-nanotubenonvolatile nanotube diode with a Schottky diode and PN diode inparallel and with both Schottky and PN parallel diodes in series with avertically oriented nonvolatile nanotube switch within vertical cellboundaries.

FIG. 32 illustrates methods of fabrication of stacked 3D memory arraysusing both cathode-to-nanotube and anode-to-nanotube nonvolatilenanotube diodes similar to those illustrated schematically in FIGS. 12and 13, according to some embodiments.

FIG. 33A illustrates a perspective view of an embodiment of two stacked3D memory arrays using both cathode-to-nanotube and anode-to-nanotube 3Darrays.

FIGS. 33B & 33B′ illustrate cross sectional views of two embodiments ofstacked 3D memory array structures with a shared word line.

FIG. 33C illustrates a cross sectional view of an embodiment of astacked 3D memory array structure which is a variation of the structureillustrated in FIG. 33B.

FIG. 33D illustrates operational waveforms for the memory structuresillustrated in FIGS. 33A, 33B, and 33B′, according to some embodiments.

FIGS. 34A-34FF illustrate methods of fabrication for cathode-on-nanotubememory cross sectional structures with vertically oriented nonvolatilenanotube switches within vertical cell boundaries illustrated in FIGS.28A and 28B, according to some embodiments.

FIGS. 35A-35S illustrate methods of fabrication for cathode-on-nanotubememory cross sectional structures with horizontally oriented nonvolatilenanotube switches within vertical cell boundaries illustrated in FIG.28C, according to some embodiments.

FIGS. 36A-36FF illustrate methods of fabrication for anode-on-nanotubememory cross sectional structures with vertically oriented nonvolatilenanotube switches within vertical cell boundaries illustrated in FIGS.32A, 32B and 32C, according to some embodiments.

FIG. 37 illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with a cathode-to-nanotube oranode-to-nanotube nonvolatile nanotube diode, with the diode portion ofthe structure represented schematically in series with anear-cell-centered placement of a vertically oriented nonvolatilenanotube switch within vertical cell boundaries.

FIG. 38 illustrates an embodiment of a nanotube layer formed on asubstrate by spray-on methods with relatively small void areas.

FIG. 39 illustrates an embodiment similar to that shown in FIG. 37 witha thicker nonvolatile nanotube switch including a nanotube element withoff-cell-centered placement within vertical cell boundaries.

FIG. 40 illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with a cathode-to-nanotube oranode-to-nanotube nonvolatile nanotube diode, with the diode portion ofthe structure represented schematically in series with a nonvolatilenanotube switch including a nanotube element within vertical cellboundaries and filling the region within the cell boundaries.

FIGS. 41A-41B illustrate a representation of a method of formingcontrolled shapes within and on vertical sidewalls of concave (trench)structures, according to some embodiments.

FIGS. 42A-42H illustrate methods of fabricating nonvolatile nanotubeswitches having nanotube elements outside cell boundary regions andwithin and on vertical sidewalls of trench structures, according to someembodiments.

FIGS. 43A-43C illustrate embodiments of nonvolatile nanotube switcheshaving nanotube elements of varying thickness outside cell boundaryregions and within and on vertical sidewalls of trench structures.

FIGS. 44A-44B illustrate embodiments of nonvolatile nanotube switcheshaving nanotube elements of varying thickness both within cell boundarycell regions and outside cell boundary cell regions, but within and onvertical sidewalls of trench structures.

FIG. 45 illustrates a variation of the embodiments of FIGS. 43A-43C inwhich two nonvolatile nanotube switches share a single select (steering)diode to form a double dense 3D memory array without stacking two arraysas illustrated in FIGS. 33B, 33B′, and 33C.

FIG. 46 illustrates a variation the embodiments of FIGS. 44A-44B inwhich two nonvolatile nanotube switches share a single select (steering)diode to form a double dense 3D memory array without stacking two arraysas illustrated in FIGS. 33B, 33B′, and 33C.

FIG. 47 illustrates a three dimensional cross section of an embodimentof a dense 3D cell structure formed with a cathode-to-NT nonvolatilenanotube diode with a Schottky diode in series with ahorizontally-oriented self-aligned end-contacted nanotube switchconnected to contact regions using trench sidewall wiring.

FIGS. 48A-48BB illustrate a method of fabrication of the structure inFIG. 47 using a trench fill conductor approach to generating trenchsidewall wiring, according to some embodiments.

FIG. 49 illustrates an embodiment of a nonvolatile nanotube switch in anessentially horizontal orientation in which two terminals are providedat opposite ends of a patterned nanotube channel element, and onlycontacting said nanotube element end regions.

FIG. 50 illustrates the operation of the switch of FIG. 49, according tosome embodiments.

FIGS. 51 and 52 illustrate corresponding three dimensional crosssections of embodiments of dense 3D cell structures formed with ananode-to-NT nonvolatile nanotube diode with a Schottky diode in serieswith a horizontally-oriented self-aligned end-contacted nanotube switchconnected to contact regions using trench sidewall wiring.

FIG. 53 illustrates a perspective view of an embodiment of stackedtwo-high memory array using cathode-on-NT and anode-on-NT stackedarrays.

FIGS. 54A-54B illustrate cross sections of embodiments of two highmemory arrays using the 3D memory structures of FIGS. 47, 48, 51, and52.

FIGS. 55A-55F illustrate cross sections of 3D memory cells usingsidewall wiring formed using conformal conductor deposition insidetrench openings instead of trench fill methods used in FIGS. 47,48A-48BB, 51, and 52, according to some embodiments.

FIGS. 56A-56F illustrate perspective drawings of embodiments ofnonvolatile nanotube switches including switch contact locations atopposite ends of the nanotube element, and embodiments of nonvolatilenanotube block-based switches with contacts located at top, bottom, andend locations.

FIGS. 57A-57C illustrate perspective drawings of embodiments ofnonvolatile nanotube block-based switches with top and bottom contactlocations and various insulator options.

FIGS. 58A-58D illustrate a cross section drawing and an SEM view of anembodiment of a nonvolatile nanotube block-based switch with top, side,and end contacts.

FIG. 59 illustrates electrical ON/OFF switching characteristics for thenonvolatile nanotube block-based switch embodiment illustrated in FIGS.58A-58D.

FIGS. 60A-60C illustrate a cross sectional drawing and an SEM image ofan embodiment of a nonvolatile nanotube block-based switch with end-onlycontacts.

FIG. 61 illustrates the near-ohmic electrical resistance of thenonvolatile nanotube block-based switch embodiment illustrated in FIGS.60A-60C in the ON state.

FIGS. 62A-62B illustrate a cross sectional drawing of an embodiment of anonvolatile nanotube block-based switch with a bottom contact and acombined top and end contact.

FIGS. 63A-63B illustrate electrical ON/OFF switching characteristics ofthe nonvolatile nanotube block-based switch embodiment illustrated inFIGS. 62A-62B.

FIGS. 64A-64C illustrate a plan view drawing, a cross sectional drawing,and an SEM image of an embodiment of a nonvolatile nanotube block-basedswitch with top and bottom contacts.

FIG. 65 illustrates electrical ON/OFF switching characteristics of thenonvolatile nanotube block-based switch embodiment illustrated in FIGS.64A-64C.

FIGS. 66A-66C illustrate methods of fabrication of nonvolatile nanotubeblocks using various nanotube solution types and insulators, accordingto some embodiments.

FIG. 67 illustrates a three dimensional cross section along the wordline (X-direction) of an embodiment of a dense 3D cell structure formedwith cathode-to-NT nonvolatile nanotube diodes, with the diode portionof the structure in series with a nonvolatile nanotube block-basedswitch including a nonvolatile nanotube block within vertical cellboundaries and filling the region within the cell boundaries.

FIGS. 68A-68I illustrate methods of fabrication of cathode-on-nanotubememory cross sectional structures with nonvolatile nanotube diodes thatinclude nonvolatile nanotube block-based switches within vertical cellboundaries such as those illustrated in FIGS. 67 and 40, according tosome embodiments.

FIG. 69 illustrates a three dimensional cross sectional view along thebit line (Y-direction) of an embodiment of a dense 3-D cell structureformed with anode-to NT nonvolatile nanotube diodes, with the diodeportion of the structure in series with a nonvolatile nanotubeblock-based switch including a nonvolatile nanotube block withinvertical cell boundaries and filling the region within the cellboundaries.

FIG. 70 illustrates a three dimensional cross sectional view along theword line (X-direction) of an embodiment of a dense 3-D cell structureformed with anode-to NT nonvolatile nanotube diodes with the diodeportion of the structure in series with a nonvolatile nanotubeblock-based switch including a nonvolatile nanotube block withinvertical cell boundaries and filling the region within the cellboundaries.

FIG. 71 illustrates a 3D perspective drawing of an embodiment of atwo-high stack of three dimensional nonvolatile nanotube block-basedswitches with top and bottom contacts, and word lines shared betweenupper and lower arrays.

FIG. 72A illustrates a three dimensional cross sectional view along wordlines (X-direction) of an embodiment of a two-high stack of threedimensional nonvolatile nanotube block-based switches with top andbottom contacts, and word lines shared between upper and lower arrays.

FIG. 72B illustrates a three dimensional cross sectional view along bitlines (Y-direction) of an embodiment of a two-high stack of threedimensional nonvolatile nanotube block-based switches with top andbottom contacts and word lines shared between upper and lower arrays.

FIG. 73 illustrates a 3D perspective drawing of an embodiment of atwo-high stack of three dimensional nonvolatile nanotube block-basedswitches with top and bottom contacts, with no array lines, such as wordlines, shared between upper and lower arrays.

FIG. 74 illustrates a three dimensional cross sectional view along wordlines (X-direction) of an embodiment of a two-high stack of threedimensional nonvolatile nanotube block-based switches with top andbottom contacts, and no array lines, such as word lines, shared betweenupper and lower arrays.

FIG. 75 illustrates a 3-D perspective of an embodiment of a nonvolatilememory array including four 3-D nonvolatile memory cells, with each cellincluding a 3-D nonvolatile nanotube diode including a nonvolatilenanotube block-based switch, and cell interconnections formed by bitlines and word lines.

FIGS. 76A-76D illustrate methods of fabrication of a cathode-on-nanotubememory cross sectional structure with nonvolatile nanotube diodes thatinclude nonvolatile nanotube block-based switches within vertical cellboundaries, such as those illustrated in FIG. 75, according to someembodiments.

FIG. 77 illustrates a 3D perspective drawing of an embodiment of amulti-level high stack of three dimensional nonvolatile nanotubeblock-based switches with top and bottom contacts, with no array lines,such as word lines, shared between upper and lower arrays.

DETAILED DESCRIPTION

Embodiments of the present invention provide nonvolatile diodes andnonvolatile nanotube blocks and systems using same and methods of makingsame.

Some embodiments of the present invention provide 3-D cell structuresthat enable dense nonvolatile memory arrays that include nanotubeswitches and diodes, can write logic 1 and 0 states for multiple cycles,and are integrated on a single semiconductor (or other) substrate. Itshould be noted that such nonvolatile memory arrays may also beconfigured as NAND and NOR arrays in PLA, FPGA, and PLD configurationsfor performing stand-alone and embedded logic functions as well.

Some embodiments of the present invention provide diode devices havingnonvolatile behavior as a result of diodes combined with nonvolatilenanotube components, and methods of forming such devices.

Some embodiments of the present invention also provide nanotube-basednonvolatile random access memories that include nonvolatile nanotubediode device cells having a relatively high density, and methods offorming such memory devices.

Some embodiments of the invention provide nonvolatile devices thatcombine nonvolatile nanotube switches (NV NT Switches), such as thosedescribed in U.S. patent application Ser. No. 11/280,786, with diodes ina nonvolatile nanotube diode (NV NT Diode) device.

Suitable diodes include Schottky, PN, PIN, PDB (planar-doped-barrier),Esaki, LED (light emitting), laser and other diodes and FET diodes.Combinations of NV NT switches with PDB and Esaki diodes may be used infast switching applications, while combinations of NV NT switches andLED and Laser diodes may be used in light (photon) sources forcommunications and display applications, as well as photon-based logicand memory applications. Nonvolatile nanotube diodes (NV NT Diodes)formed using various diode and NV NT Switch combinations, such ascathode-to-nanotube and anode-to-nanotube interconnections, aredescribed. NV NT Diode operation is also described. Devices fabricatedusing NV NT Diodes are also described.

While in some embodiments, NV NT diodes are formed by combining NV NTswitches and various diodes formed using silicon and metallurgiestypical of CMOS processes, a wide variety of semiconductor materials andconductors may be used to form a variety of diodes in combination with awide variety of conductors. Examples of semiconductor materials are Si,Ge, SiC, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, CdS, CdSe, CdTefor example. Schottky diodes may be formed by combining varioussemiconductor material with compatible conductors such as Al, Ag, Au,Au/Ti, Bi, Ca, Co, CoSi₂, Cr, Cu, Fe, In, Ir, Mg, Mo, MoSi₂, Na, Ni,NiSi₂, Os, Pb, Pd, Pd₂Si, Pt, PtSi, Rh, RhSi, Ru, Sb, Sn, Ti, TiSi₂, W,WSi₂, Zn, ZrSi₂, and others for example. LED and laser diodes may beformed using such semiconductor material as GaInAsPt, GaAsSb, InAsP,InGaAs, and many other combinations of materials that determine lightemission wavelength.

Alternatively, FET diodes may be formed by combining a NV NT Switch anda three terminal FET with gate electrically connected to one of the twodiffusion terminals to form a two terminal FET diode device. Whencombining a NV NT Switch and an FET diode, a nonvolatile nanotube diodemay also be referred to as a nonvolatile nanotube FET-diode, abbreviatedas NV NT FET-Diode, to highlight this difference with respect toSchottky, PN, PIN, and other diodes. However, differences betweencombinations of NV NT Switches and FET diodes and Schottky, PN, PIN andother diodes may not be highlighted and all may be referred to a NV NTDiode.

Embodiments of 2-D nonvolatile memories, both stand-alone and embeddedin logic (processors for example), that use nonvolatile nanotube diodes(NV NT Diodes) as storage elements, are also described. These NV NTDiodes may be formed in and/or on a semiconductor substrate with memorysupport circuits and logic function and integrated on a single substratesuch as a semiconductor chip or wafer to form 2-D memory and 2-D memoryand logic functions.

Embodiments of 3-D architectures of nonvolatile memories, bothstand-alone and embedded in logic, that use NV NT Diodes as 3-D cellsfor 3-D memory arrays that can write logic 1 and 0 states for multiplecycles, are also described. It should be noted that some embodiments of3-D memories using arrays of NV NT diode cells are described withrespect to memory arrays that are not fabricated in or on asemiconductor substrate, but are instead formed on an insulating layerabove support circuits formed in and on a semiconductor substrate withinterconnections between support circuits and the 3-D memory array.

NV NT Diode arrays can also be formed on a planar insulating surface,above support circuits with array interconnections through and on theinsulating layer, in which the NV NT Diode arrays are formed usingmethods of fabrication in which array features are self-aligned in bothX and Y directions such that array features are not increased in size toaccommodate alignment requirements.

It should also be noted that presently available planarizationtechniques (chemical-mechanical planarization (CMP), for example)combined with Silicon-on-Insulator (SOI) technology and thin filmtransistor (TFT) technology enable 3-D memory arrays using NV NT Diodesas 3-D cells to be fabricated in planar dense stacked structures above asingle substrate in which the substrate is not a semiconductorsubstrate. Combined planarization techniques anddisplay-application-driven enhanced TFT technology enablenon-semiconductor substrates such as glass, ceramic, or organicsubstrate as alternatives to using semiconductor substrates.

Methods of fabrication of various 3-D memories are described.

Although NV NT Diode-based nonvolatile memories are described, it shouldbe noted that such nonvolatile memory arrays may also be configured asNAND and NOR arrays in PLA, FPGA, and PLD functions for performingstand-alone and embedded logic as well.

Two Terminal Nonvolatile Nanotube Diode Devices

Some embodiments provide a nonvolatile nanotube diode device that actslike a diode in its ability to direct electronic communication in aforward biased direction, and prevent communication in a reversedirection, if the nanotube diode is in a conductive (ON) mode (orstate). However, if a nonvolatile nanotube diode device is in anonconductive (OFF) mode (or state), then direct communication isprevented in either forward or reverse direction. The nonvolatilenanotube diode device conductive (ON) mode or nonconductive (OFF) modeis nonvolatile and is maintained without power supplied to the device.The mode of the nonvolatile nanotube diode device may be changed from ONto OFF or from OFF to ON by applying suitable voltage and current levelsusing a stimulus circuit.

Some embodiments of the nonvolatile device are formed by combiningnonvolatile nanotube switches (NV NT Switches) described in U.S. patentapplication Ser. No. 11/280,786, U.S. patent application Ser. No. (TBA),entitled “Nonvolatile Resistive Memories Having Scalable Two-TerminalNanotube Switches,” filed on even date herewith, and/or U.S. patentapplication Ser. No. (TBA), entitled “Memory Elements and Cross PointSwitches and Arrays of Same Using Nonvolatile Nanotube Blocks,” filed oneven date herewith, and diodes such as Schottky, PN, PIN, and otherdiodes and FET diodes to form a nonvolatile nanotube diode (NV NT Diode)device. In some embodiments, nonvolatile nanotube diodes (NV NT Diodes)are two terminal devices having one terminal in contact with oneterminal of a nonvolatile nanotube switch and another terminal incontact with the anode or cathode of a diode. In some embodiments, ashared internal contact connects a second terminal of a nonvolatilenanotube switch with the cathode or anode of a diode to form thenonvolatile nanotube diode device.

Some embodiments of NV NT diodes are scalable to large nonvolatile arraystructures. Some embodiments use processes that are compatible with CMOScircuit manufacture. It should be noted that based on the principle ofduality in semiconductor devices, P and N regions in the examplesillustrated may be interchanged with corresponding changes in thepolarity of applied voltages.

Nonvolatile Nanotube Diode Devices Having the Cathode of the DiodeConnected to One Terminal of the Nonvolatile Nanotube Switch; and OtherNonvolatile Nanotube Diode Devices Having the Anode of the DiodeConnected to One Terminal of the Nonvolatile Nanotube Switch

Nonvolatile nanotube switches (NV NT Switches) are described in detailin U.S. patent application Ser. No. 11/280,786, and are summarizedbriefly below. NV NT Switches include a patterned nanotube element andtwo terminals in contact with the patterned nanotube (nanofabric)element. Methods of forming nanotube fabrics and elements, andcharacteristics thereof, are described in greater detail in theincorporated patent references. Nonvolatile nanotube switch operationdoes not depend on voltage polarity, positive or negative voltages maybe used. A first terminal may be at a higher or lower voltage withrespect to a second terminal. There is no preferential current flowdirection. Current may flow from a first to a second terminal or from asecond to a first terminal.

FIG. 3 illustrates an embodiment of a NV NT Switch 300 including apatterned nanotube element 330 on insulator 340 which is supported bysubstrate 350. Terminals (conductive elements) 310 and 320 are depositeddirectly onto patterned nanotube element 330 and at least partiallyoverlap opposite ends of patterned nanotube element 330. The nonvolatilenanotube switch channel length L_(SW-CH) is the separation between 310and 320. L_(SW-CH) is important to the operation of nonvolatile nanotubeswitch 300 as described further below. Substrate 350 may be an insulatorsuch as ceramic or glass, a semiconductor, or an organic rigid orflexible substrate. Substrate 350 may be also be organic, and may beflexible or stiff. Insulator 340 may be SiO₂, SiN, Al₂O₃, or anotherinsulator material. Terminals (contacts) 310 and 320 may be formed usinga variety of contact and interconnect elemental metals such as Ru, Ti,Cr, Al, Al(Cu), Au, Pd, Ni, W, Cu, Mo, Ag, In, Ir, Pb, Sn, as well asmetal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides, oxides, or silicides such as RuN,RuO, TiN, TaN, CoSi_(x) and TiSi_(x).

FIG. 4 illustrates an embodiment of a NV NT Switch 400 includingpatterned nanotube element 430 on insulator 440 which is supported bysubstrate 450. Patterned nanotube element 430 is a nonplanar conformalnanofabric that also partially overlaps and contacts terminals(conductive elements) 410 and 420 on top and side surfaces. Terminals(contacts) 410 and 420 are deposited and patterned directly ontosubstrate 450 prior to patterned nanotube element 430 formation.Patterned nanotube element 330 is formed using a conformal nanofabricthat at least partially overlaps terminals 410 and 420. The nonvolatilenanotube switch channel length L_(SW-CH) is the separation betweenterminal 410 and 420. L_(SW-CH) is important to the operation ofnonvolatile nanotube switch 400 as described further below. Substrate450 may be an insulator such as ceramic or glass, a semiconductor, or anorganic rigid or flexible substrate. Substrate 450 may be also beorganic, and may be flexible or stiff. Insulator 440 may be SiO₂, SiN,Al₂O₃, or another insulator material. Terminals 410 and 420 may beformed using a variety of contact and interconnect elemental metals suchas Ru, Ti, Cr, Al, Al(Cu), Au, Pd, Ni, W, Cu, Mo, Ag, In, Ir, Pb, Sn, aswell as metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, othersuitable conductors, or conductive nitrides, oxides, or silicides suchas RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).

FIG. 5 illustrates an embodiment of a NV NT Switch 500 includingpatterned nanotube element 530 on insulator 535, which is on insulator540, which is supported by substrate 550. Patterned nanotube element 530is a nanofabric on a planar surface that also partially overlaps andcontacts terminals (conductive elements) 510 and 520. Terminals(contacts) 510 and 520 are deposited and patterned directly ontosubstrate 550 prior to patterned nanotube element 530 formation.Patterned nanotube element 530 to terminal 520 overlap distance 560 doesnot significantly change nonvolatile nanotube switch 500 operation. Thenonvolatile nanotube switch channel length L_(SW-CH) is the separationbetween terminal 510 and 520. L_(SW-CH) is important to the operation ofnonvolatile nanotube switch 500 as described further below. Substrate550 may be an insulator such as ceramic or glass, a semiconductor, or anorganic rigid or flexible substrate. Substrate 550 may be also beorganic, and may be flexible or stiff. Insulators 535 and 540 may beSiO₂, SiN, Al₂O₃, or another insulator material. Terminals 510 and 520may be formed using a variety of contact and interconnect elementalmetals such as Ru, Ti, Cr, Al, Al(Cu), Au, Pd, Ni, W, Cu, Mo, Ag, In,Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu, TiPd, PbIn, andTiW, other suitable conductors, or conductive nitrides, oxides, orsilicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).

In some embodiments, NV NT Switch 500 may be modified (not shown) toinclude a gap region in insulator 535 between a portion of nanotubeelement 530 and insulator 540 as described further in U.S. patentapplication Ser. No. (TBA), entitled “Nonvolatile Resistive MemoriesHaving Scalable Two-Terminal Nanotube Switches,” and/or U.S. patentapplication Ser. No. (TBA), entitled “Memory Elements and Cross PointSwitches and Arrays of Same Using Nonvolatile Nanotube Blocks,” filed oneven date herewith. Without wishing to be bound by theory, it isbelieved that in the suspended region a reduced amount of heat is lostto the surrounding substrate, so smaller values of voltage and currentmay be required to heat the nanotubes to a temperature sufficient forswitching to occur. Other mechanisms are possible.

FIG. 6A illustrates a SEM image of an embodiment of a nonvolatilenanotube switch 600 prior to passivation and corresponding tononvolatile nanotube switch 300 shown in cross sectional drawing 300 inFIG. 3. Nonvolatile nanotube switch 600 includes patterned nanotube(nanofabric) element 630, terminals (contacts) 610 and 620, andinsulator 640. Exemplary nonvolatile nanotube switches 600 have beenfabricated with terminal-to-terminal channel lengths (L_(SW-CH)) in therange of 250 nm to 22 nm thereby reducing nonvolatile nanotube switchsize and lowering erase (write 0) voltages at shorter channel lengths,as illustrated further below. Programming (write 1) voltages typicallyremain lower than erase (write 0) voltages. Erase voltage measurementson nonvolatile nanotube switches of varying channel width (data notshown) indicate no significant dependence of erase voltage on devicechannel width as the channel width W_(SW-CH) is varied from 500 to 150nm. Erase voltage measurements on nonvolatile nanotube switches ofvarying nanofabric-to-contact terminal overlap lengths (data not shown)indicate no significant dependence of erase voltage on overlap lengths,such as overlap length 660 in FIG. 6A, as overlap lengths are variedfrom approximately 800 to 20 nm.

FIGS. 6A and 6B were obtained using SEM voltage contrast imaging of NVNT Switch 600 including patterned nanotube element 630 connected toterminals 610 and 620. With respect to FIG. 6A, NV NT Switch 600 is inan ON state such that voltage applied to terminal 620 is transmitted toterminal 610 by patterned nanotube element 630 in an electricallycontinuous ON state. FIG. 6B illustrates NV NT Switch 600′, whichcorresponds to NV NT Switch 600 in the OFF state. In the OFF state,patterned nanotube element 630 is electrically discontinuous withinitself and/or separates from one of the terminals 610, 620. SEM voltagecontrast imaging of NV NT Switch 600′ in FIG. 6B illustrates patternednanotube element 630 in which patterned nanotube element region 630′appears to be electrically connected to terminal 620 (light region) andpatterned nanotube element region 630″ appears to be electricallyconnected to terminal 610′ (dark region), but where patterned nanotubeelement regions 630′ and 630″ appear not to be electrically connected toeach other, i.e., the patterned nanotube element 630 “breaks.” Terminal610′ is dark since voltage applied to terminal 620 does not reachterminal 610′ because of the apparent electrical discontinuity betweenpatterned nanotube element regions 630′ and 630″. Note that terminal610′ is the same as terminal 610, except that it is not electricallyconnected to terminal 620 in NV NT Switch 600′.

Nonvolatile nanotube switch embodiment 600 illustrated in FIGS. 6A-6B isfabricated on a horizontal surface. In general, patterned nanotubeelements can be fabricated using conformal patterned nanofabrics thatmay be oriented at various angles, without limitations, as described ingreater detail in the incorporated patent references. FIG. 7A is an SEMimage of exemplary structure 700 with nanofabric 730 conforming to anunderlying step after deposition, with a vertical orientation 735region. These conformal properties of nanofabrics may be used tofabricate vertically oriented nonvolatile nanotube switches withenhanced dimensional control and requiring less area (e.g. can befabricated at greater density) as illustrated further below.

FIG. 7B is a representation of an embodiment of 3-D memory cell crosssection 750 storage elements described in greater detail in U.S. patentapplication Ser. No. 11/280,786. 3D memory cell storage regions 760A and760B are mirror image storage devices using nonvolatile nanotubeswitches with vertically-oriented nanotube elements 765 and 765′.Protective insulator materials 770 and 770′, and 775, 775′, and 775″ areused to enhance the performance and reliability of nanotube elements 765and 765′, respectively. Memory cell storage regions 760A and 760Binclude lower contacts 780 and 780′, respectively, and upper contacts785 and 785′, respectively. Upper contacts 785 and 785′ include sidewalland top surface contact regions. Contacts 780 and 780′ are embedded ininsulator 790. Insulator 795 on the top surface of insulator 790includes sidewall regions used to define the location of nanotubechannel elements 765 and 765′.

FIG. 8 illustrates a nonvolatile nanotube switch 800 schematicrepresentation of nonvolatile nanotube switches 300, 400, 500 and othernonvolatile nanotube switches (not shown) having that may includesuspended regions and also may include horizontal, vertical, or otherorientation, according to some embodiments. Two terminals (contacts) 810and 820 are illustrated, and correspond, for example to terminals(contacts) 310 and 320 of NV NT Switch 300; 410 and 420 of NV NT Switch400; and 510 and 520 of NV NT Switch 500 for example.

Laboratory testing results of individual fabricated nonvolatile nanotubeswitches, represented schematically by nonvolatile nanotube switch 800illustrated in FIG. 8, are illustrated by graph 900 in FIG. 9A.Nonvolatile nanotube switch 800 switching results for more than 50million ON/OFF cycles illustrated by graph 900 shows that the conductingstate resistance (ON Resistance) is in the range of 10 kOhms to 50kOhms, while the nonconducting state resistance (OFF Resistance) exceeds10 GOhm, for greater than five orders of magnitude separation ofresistance values between conducting and nonconducting states.Nonvolatile nanotube switch 800 has a patterned nanotube element with achannel length (L_(SW-CH)) of 250 nm. At channel lengths of 250 nm,nonvolatile nanotube switches have typical erase voltages of 8 volts andtypical program voltages of 5 volts as described further below and inU.S. patent application Ser. No. 11/280,786 and U.S. patent applicationSer. No. (TBA), entitled “Nonvolatile Resistive Memories Having ScalableTwo-Terminal Nanotube Switches,” filed on even date herewith.

FIG. 9B illustrates cycling data 900′ on fabricated devices havingchannel length of approximately 22 nm and channel width of approximately22 nm. Devices with channel lengths of approximately 20 nm typicallyhave erase voltages in the 4 to 5 volt range. The particular devicescharacterized in FIG. 9B have an erase voltage of 5 Volts, a programmingvoltage of 4 Volts, and was subjected to 100 erase/program cycles. TheON resistance is well under 100 kOhms, and the OFF resistance is wellabove 100 MOhms.

FIG. 10 curves 1000 illustrate the voltage scaling effect of channellength L_(SW-CH) reduction on erase voltage for a plurality offabricated nonvolatile nanotube switches as L_(SW-CH) is reduced fromover 250 nm to 50 nm. L_(SW-CH) refers to switch channel length asdescribed with respect to FIGS. 3, 4, and 5. The effectiveness ofchannel length reduction is illustrated in terms of erase voltage as afunction of channel length reduction and erase/program cycling yield,where each data point represents 22 devices and the number of ON/OFFerase/program cycles is five. Erase voltage is a strong function ofchannel length and is reduced (scaled) from 8 volts to 5 volts as thenonvolatile nanotube switch channel length is reduced from 250 to 50 nmas illustrated by curves 1000 shown in FIG. 10. Correspondingprogramming voltages (not shown) are less than erase voltages, typicallyin the range of 3 to 5 volts, for example. Erase voltage measurements onnonvolatile nanotube switches of varying channel width (data not shown)indicate no significant dependence of erase voltage on device channelwidth as the channel width is varied from 500 to 150 nm. Erase voltagemeasurements on nonvolatile nanotube switches of varyingnanofabric-to-contact terminal overlap lengths (data not shown) indicateno significant dependence of erase voltage on overlap lengths, such asoverlap length 660 in FIG. 6A, as overlap lengths are varied fromapproximately 800 to 20 nm.

FIG. 11A shows exemplary erase waveforms 1100 of erase voltage andcorresponding erase current as a function of time for a fabricatednonvolatile nanotube switch having a channel length of 250 nm with anerase voltage of 8 Volts and a corresponding erase current of 15micro-Amperes. Note that a negative voltage was applied to thenonvolatile nanotube switch under test. Nonvolatile nanotube switcheswill work with positive or negative applied voltages and current flow ineither direction. Erase currents are typically in the range of 1 to 50uA, depending on the number of activated SWNTs in the patterned nanotubeelement in the channel region. Erase currents as the switch transitionsfrom an ON state to an OFF state are typically not limited by a stimuluscircuit.

FIG. 11B shows exemplary waveforms 1100′ of a full nonvolatile nanotubeswitch cycle including read, erase, and program operations. Erasewaveforms show erase voltage and corresponding erase current as afunction of time for a fabricated nonvolatile nanotube switch having achannel length of 250 nm, with an erase voltage of 8 Volts and acorresponding erase current of 10 micro-Amperes. Programming waveformsshow program voltage and corresponding program current as a function oftime for a nonvolatile nanotube switch having a channel length of 250nm, with a program voltage of 5 Volts and a corresponding programcurrent of 25 micro-Amperes. Programming currents as the switchtransitions from an OFF state to an ON state are typically limited bythe stimulus circuit to improve programming characteristics. Examples ofprogramming current limitation using stimulus circuits are described inU.S. patent application Ser. No. (TBA), entitled “Nonvolatile ResistiveMemories Having Scalable Two-Terminal Nanotube Switches,” filed on evendate herewith. The erase waveforms illustrated in FIG. 11A and the read,erase, and program waveform in FIG. 11B are described in more detail inU.S. patent application Ser. No. 11/280,786.

Nonvolatile nanotube switches may be fabricated to exhibit a wide rangeof ON Resistance values depending on switch channel length, and thenumber of individual nanotubes in the patterned nanotube (channel)element. Nonvolatile nanotube switches may exhibit ON Resistances in the1 kOhm to 10 MOhm range, while OFF Resistance is typically 100 MOhm or 1GOhm or greater

Nonvolatile nanotube diode devices are a series combination of a twoterminal semiconductor diodes and two terminal nonvolatile nanotubeswitches similar to nonvolatile nanotube switches described furtherabove with respect to FIGS. 3 to 11. Various diode types are describedin the reference NG, K. K., “Complete Guide to Semiconductor Devices”Second Edition, John Wiley and Sons, 2002, the entire contents of whichare incorporated herein by reference; Schottky diodes (Schottky-barrierdiodes) are described in pp. 31-41; junction (PN) diodes are describedin pp. 11-23; PIN diodes are described in pp. 24-41; light emittingdiodes (LEDs) pp. 396-407. FET-diodes are described in the referenceBaker, R. J. et al. “CMOS Circuit Design, Layout, and Simulation”, IEEEPress, 1998, pp. 168-169, the entire contents of which are incorporatedherein by reference.

NV NT Diode embodiments described further below typically use Schottkydiodes, PN diodes and FET-diodes. However, other diode types such as PINdiodes may be combined with nonvolatile nanotube switches to formnonvolatile nanotube PIN-diodes that may enable or disable RF switching,attenuation and modulation, signal limiting, phase shifting, powerrectification, and photodetection for example. Also, nonvolatile LEDdiodes may be combined with nonvolatile switches to form nonvolatilenanotube LED-diodes that enable or disable LED diodes and provide lightoutput patterns stored as nonvolatile states in a nonvolatile nanotubeLED-diode.

Schottky diodes typically have low forward-voltage drops, which is anadvantage, and good high frequency characteristics. These characteristicplus ease of fabrication make Schottky diodes useful in a wide range ofapplications. A critical step in the fabrication is to prepare a cleansurface for intimate contact of the metal to the semiconductor surface.Metal-on-silicon or metal silicides-on-silicon may also be used.Schottky diodes 142 illustrated in FIG. 1 and described further aboveand in the reference U.S. Pat. No. 4,442,507 used platinum to form aplatinum silicide-on-silicon Schottky diode having a forward ON-voltageof approximately 0.4 volts and a reverse breakdown voltage ofapproximately 10 volts. Nonvolatile nanotube diodes described furtherbelow may be fabricated with nonvolatile nanotube switches and Schottky,PN, P-I-N, LED and other diodes such as FET-diodes in series dependingon application requirements.

FIG. 12 illustrates an embodiment of a nonvolatile nanotube diode 1200device formed by combining diode 1205 and nonvolatile nanotube switch1210 in series. Terminal T1 is connected to anode 1215 of diode 1205 andterminal T2 is connected to contact 1225 of nonvolatile nanotube switch1210. Cathode 1220 of diode 1205 is connected to contact 1230 ofnonvolatile nanotube switch 1210 by contact 1235. The operation ofnonvolatile nanotube diode 1200 will be explained further below.

FIG. 13 illustrates an embodiment of a nonvolatile nanotube diode 1300device formed by combining diode 1305 and nonvolatile nanotube switch1310 in series. Terminal T1 is connected to cathode 1320 of diode 1305and terminal T2 is connected to contact 1325 of nonvolatile nanotubeswitch 1310. Anode 1315 of diode 1305 is connected to contact 1330 ofnonvolatile nanotube switch 1310 by contact 1335.

FIG. 14 illustrates an embodiment of a nonvolatile nanotube diode 1400device formed by combining NFET diode 1405 and nonvolatile nanotubeswitch 1410 in series. Terminal T1 is connected to contact 1415 of NFETdiode 1405 and terminal T2 is connected to contact 1425 of nonvolatilenanotube switch 1410. Contact 1415 is wired to both gate and a firstdiffusion region of an NFET to form a first NFET diode 1405 terminal. Asecond diffusion region 1420 forms a second terminal of NFET diode 1405.Second diffusion region 1420 of NFET diode 1405 is connected to contact1430 of nonvolatile nanotube switch 1410 by contact 1435.

FIG. 15 illustrates an embodiment of a nonvolatile nanotube diode 1500device formed by combining NFET diode 1505 and nonvolatile nanotubeswitch 1510 in series. Terminal T1 is connected to a first NFETdiffusion terminal 1515 of NFET diode 1505 and terminal T2 is connectedto contact 1525 of nonvolatile nanotube switch 1510. Contact 1520 iswired to both gate and a second diffusion region of an NFET to form asecond NFET diode 1505 terminal. Contact 1520 of NFET diode 1505 isconnected to contact 1530 of nonvolatile nanotube switch 1510 by contact1535. The operation of nonvolatile nanotube diode 1200 will be explainedfurther below.

FIG. 16 illustrates an embodiment of a nonvolatile nanotube diode 1600device formed by combining PFET diode 1605 and nonvolatile nanotubeswitch 1610 in series. Terminal T1 is connected to a first PFETdiffusion terminal 1615 of PFET diode 1605 and terminal T2 is connectedto contact 1625 of nonvolatile nanotube switch 1610. Contact 1620 iswired to both gate and a second diffusion region of a PFET to form asecond PFET diode 1605 terminal. Contact 1620 of PFET diode 1605 isconnected to contact 1630 of nonvolatile nanotube switch 1610 by contact1635.

FIG. 17 illustrates an embodiment of a nonvolatile nanotube diode 1700device formed by combining PFET diode 1705 and nonvolatile nanotubeswitch 1710 in series. Terminal T1 is connected to contact 1715 of PFETdiode 1705 and terminal T2 is connected to contact 1725 of nonvolatilenanotube switch 1710. Contact 1715 is wired to both gate and a firstdiffusion region of a PFET to form a first PFET diode 1705 terminal. Asecond diffusion region 1720 forms a second terminal of PFET diode 1705.Second diffusion region 1720 of PFET diode 1705 is connected to contact1730 of nonvolatile nanotube switch 1710 by contact 1735.

Operation of Nonvolatile Nanotube Diode Devices

FIG. 18 illustrates an embodiment of a circuit 1800 in which stimuluscircuit 1810 applies voltage V_(T1) between terminal T1 of NV NT Diode1200 and a reference terminal, ground for example, and stimulus circuit1820 applies voltage V_(T2) between terminal T2 of NV NT Diode 1200 anda reference terminal, ground for example. NV NT Diode 1200 is formed bydiode 1205 and nonvolatile nanotube switch 1210 in series as describedfurther above with respect to FIG. 12.

FIG. 19 illustrates an embodiment of a circuit 1900 in which stimuluscircuit 1910 applies voltage V_(T2) between terminal T2 of NV NT Diode1500 (or NV NT FET-Diode 1500) and a reference terminal, ground forexample, and stimulus circuit 1920 applies voltage V_(T1) betweenterminal T1 of NV NT Diode 1500 and a reference terminal, ground forexample. NV NT Diode 1500 is formed by FET diode 1505 and nonvolatilenanotube switch 1510 in series as described further above with respectto FIG. 15.

In an exemplary write 0 (erase) operation, referring to circuit 1800 inFIG. 18, nonvolatile nanotube diode 1200 transitions from an ON to anOFF state during a mode setting time interval when write 0 operationwaveforms 2000-1 are applied as illustrated in FIG. 20A. Write 0operation 2000-1 waveforms illustrate voltage V_(T1) at a low voltage,zero volts for example, prior to initiating write 0 operation 2000-1.Voltage V_(T2) may be at any voltage between zero volts andapproximately 10 volts, where 10 volts is the approximate reverse biasbreakdown voltage of NV NT Diode 1200. The reverse bias breakdownvoltage of NV NT Diode 1200 is determined by the reverse breakdownvoltage of diode 1205, which is assumed to be approximately 10 voltsbased on the reverse breakdown voltage of Schottky diode 142 illustratedin FIG. 1 and described in U.S. Pat. No. 4,442,507. Write 0 operation2000-1 is not initiated by V_(T2) because diode 1205 in a reverse biasedmode has a high impedance which reduces voltage across and limitscurrent flow through NV NT Switch 1210 such that write 0 operation2000-1 voltage conditions of 4-5 volts across the terminals of NV NTSwitch 1210 are not met and transition from an ON resistance state to anOFF resistance state does not take place. NV NT Switch 1210 ONresistance prior to the onset of an write 0 operation is typically inthe range of 10 kOhm to 100 kOhm as illustrated in FIGS. 9A and 9B.

An exemplary write 0 operation 2000-1 during a mode setting timeinterval such as illustrated in FIG. 20A begins with a transition ofvoltage V_(T2) to a low voltage such as ground. Next, voltage V_(T1)transitions to an applied write 0 voltage of 5 volts. The applied write0 voltage rise time may be relatively short such as less than 1 ns forexample, or may be relatively long, in excess of 100 us for example.Stimulus circuit 1810 applies voltage V_(T1) to terminal T1, and avoltage V_(T1) minus the forward voltage of diode 1205 is applied toterminal 1230 of nonvolatile nanotube switch 1210. If the forwardvoltage bias drop of diode 1205 is assumer to be approximately 0.5 volts(similar to a forward voltage of approximately 0.4 volts for Schottkydiodes used in U.S. Pat. No. 4,442,507), and since terminal T2 is heldat ground, then a voltage of approximately 4.5 volts appears across NVNT Switch 1210. NV NT Switch 1210 transitions from an ON state to an OFFstate if the erase threshold voltage of NV NT Switch 1210 is 4.5 volts(or less), for example. During write 0 operation 2000-1 current limitingis not required. Typical write 0 currents are less than 1 uA to 50 uA.

In an exemplary write 1 (program) operation, referring to circuit 1800in FIG. 18, nonvolatile nanotube diode 1200 transitions from an OFF toan ON state during a mode setting time interval when write 1 operationwaveforms 2000-2 are applied as illustrated in FIG. 20A. Write 1operation 2000-2 waveforms illustrate voltage V_(T1) at a low voltage;zero volts for example, prior to initiating write 0 operation 2000-2. NVNT Switch 1210 OFF resistance may be in the range of greater than 100MOhm to greater than 10 GOhm as illustrated in FIGS. 9A and 9B. Hence,diode 1205 reverse biased resistance may be less than the NV NT Switch1210 OFF resistance, and most of the applied write 1 voltage may appearacross NV NT Switch 1210 terminals 1230 and T2 illustrated in FIG. 18.If voltage V_(T2) transitions above the write 1 threshold voltage of NVNT Switch 1210, then an unwanted write 1 cycle may begin. As NV NTSwitch 1210 resistance drops, back biased diode 1205 resistance becomedominant and may prevent completion of a write 1 operation. However, inorder to prevent a partial write 1 operation, V_(T2) is limited to 4volts for example.

An exemplary write 1 operation 2000-2 during a mode setting timeinterval such as illustrated in FIG. 20A begins with a transition ofvoltage V_(T2) to a low voltage such as ground. Next, voltage V_(T1)transitions to an applied write 1 voltage of 4 volts. The applied write1 voltage rise time may be relatively short such as less than 1 ns forexample, or may be relatively long, in excess of 100 us for example.Stimulus circuit 1810 applies voltage V_(T1) to terminal T1, and avoltage V_(T1) minus the forward voltage of diode 1205 is applied toterminal 1230 of NV NT Switch 1210. If the forward voltage bias drop ofdiode 1205 is similar to a forward voltage of approximately 0.4-0.5volts such as Schottky diodes used in U.S. Pat. No. 4,442,507, and sinceterminal T2 is held at ground, then a voltage of approximately 3.5 voltsappears across NV NT Switch 1210. NV NT Switch 1210 transitions from anOFF state to an ON state if the write 1 threshold voltage of NV NTSwitch 1210 is 3.5 volts (or less), for example. During write 1operation 2000-2 current limiting can be applied. Examples of stimuluscircuits that include current limiting means are described in U.S.patent application Ser. No. (TBA), entitled “Nonvolatile ResistiveMemories Having Scalable Two-Terminal Nanotube Switches,” filed on evendate herewith. Write 1 currents are typically limited to less than 1 uAto 50 uA.

In an exemplary write 0 operation, referring to circuit 1900 in FIG. 19,nonvolatile nanotube diode 1500 (or NV NT FET-Diode 1500) transitionsfrom an ON to an OFF state during a mode setting time interval whenwrite 0 operation waveforms 2000-3 are applied as illustrated in FIG.20B. Write 0 operation 2000-3 waveforms illustrate voltage V_(T2) at alow voltage, zero volts for example, prior to initiating write 0operation 2000-3. Voltage V_(T1) may be at any voltage between zerovolts and 7 volts, where 7 volts is the reverse bias breakdown voltageof NV NT Diode 1500. The reverse bias breakdown voltage of NV NT Diode1500 is determined by the reverse breakdown voltage of FET diode 1505,which in this example is assumed to be 7 volts for an FET diodefabricated using a 0.18 um CMOS process. Write 0 operation 2000-3 is notinitiated by V_(T1) because FET diode 1505 in a reverse biased mode hasa high impedance which reduces voltage across and limits current flowthrough NV NT Switch 1510 such that write 0 operation 2000-3 voltageconditions of 4-5 volts across the terminals of NV NT Switch 1510 arenot met and transition from an ON resistance state to an OFF resistancestate does not take place. NV NT Switch 1510 ON resistance prior to theonset of an write 0 operation is typically in the range of 10 kOhm to100 kOhm as illustrated in FIGS. 9A and 9B.

An exemplary write 0 operation 2000-3 during a mode setting timeinterval such as illustrated in FIG. 20B begins with a transition ofvoltage V_(T1) to a low voltage such as ground. Next, voltage V_(T2)transitions to an applied write 0 voltage of 5 volts. The applied write0 voltage rise time may be relatively short such as 1 ns for example, ormay be relatively long, in excess of 100 us for example. Stimuluscircuit 1910 applies voltage V_(T2) to terminal T2, and a voltage V_(T2)minus the forward voltage of FET diode 1505 is applied to terminal 1530of nonvolatile nanotube switch 1510. One terminal of FET diode 1505 incircuit 1900 is connected to the lowest voltage in the circuit, groundin this example. Assuming the semiconductor substrate is also connectedto ground, the FET diode 1505 threshold voltage is not increased byvoltages applied to FET diode 1505 relative to a correspondingsemiconductor substrate. Using semiconductor fabrication methods tocontrol device characteristics such as oxide thickness and channel ionimplantation dosage, FET diode 1505 turn-on voltage may be adjusted tobe less than 0.5 volts. If the forward bias voltage drop of FET diode1505 is less than 0.5 volts, then a voltage greater than 4.5 voltsappears across NV NT Switch 1510. NV NT Switch 1510 transitions from anON state to an OFF state if the write 0 threshold voltage of NV NTSwitch 1510 is 4.5 volts (or less), for example. During write 0operation 2000-3 current limiting is not required. Typical write 0currents are less than 1 uA to 50 uA.

In an exemplary write 1 operation, referring to circuit 1900 in FIG. 19,nonvolatile nanotube diode 1500 (NV NT FET-Diode 1500) transitions froman OFF to an ON state during a mode setting time interval when write 1operation waveforms 2000-4 are applied as illustrated in FIG. 20AB.Write 1 operation 2000-4 waveforms illustrate voltage V_(T2) at a lowvoltage; zero volts for example, prior to initiating write 1 operation2000-4. NV NT Switch 1510 OFF resistance may be in the range of greaterthan 100 MOhm to greater than 10 GOhm as illustrated in FIGS. 9A and 9B.Hence, FET diode 1505 reverse biased resistance may be less than the NVNT Switch 1510 OFF resistance, and most of the applied write 1 voltagemay appear across NV NT Switch 1510 terminals 1530 and T2 illustrated inFIG. 19. If voltage V_(T1) transitions above the write 1 thresholdvoltage of NV NT Switch 1510, then an unwanted write 1 cycle may begin.As NV NT Switch 1510 resistance drops, back biased FET diode 1505resistance becomes dominant and may prevent completion of a write 1operation. However, in order to prevent a partial write 1 operation,V_(T1) is limited to 4 volts for example.

An exemplary write 1 operation 2000-4 during a mode setting timeinterval such as illustrated in FIG. 20B begins with a transition ofvoltage V_(T1) to a low voltage such as ground. Next, voltage V_(T2)transitions to an applied write 1 voltage of 4 volts. The applied write1 voltage rise time may be relatively short such as less than 1 ns forexample, or may be relatively long, in excess of 100 us for example.Stimulus circuit 1910 applies voltage V_(T2) to terminal T2, and avoltage V_(T2) minus the forward voltage of FET diode 1505 is applied toterminal 1530 of NV NT Switch 1510. One terminal of FET diode 1505 incircuit 1900 is connected to the lowest voltage in the circuit, groundin this example. Assuming the semiconductor substrate is also connectedto ground, the FET diode 1505 threshold voltage is not increased byvoltages applied to FET diode 1505 relative to a correspondingsemiconductor substrate. Using semiconductor fabrication methods tocontrol device characteristics such as oxide thickness and channel ionimplantation dosage, FET diode 1505 turn-on voltage may be adjusted tobe less than 0.5 volts. If the forward bias voltage drop of FET diode1505 is less than 0.5 volts, then a voltage greater than 4.5 voltsappears across NV NT Switch 1510. NV NT Switch 1510 transitions from anOFF state to an ON state if the write 1 threshold voltage of NV NTSwitch 1510 is 3.5 volts (or less), for example. During write 1operation 2000-4 current limiting can be applied. Examples of stimuluscircuits that include current limiting means are described in U.S.patent application Ser. No. (TBA), entitled “Nonvolatile ResistiveMemories Having Scalable Two-Terminal Nanotube Switches,” filed on evendate herewith. Write 1 currents are typically limited to less than 1 uAto 50 uA.

One alternative to using a stimulus circuit with current limiting is todesign FET diode 1505 to limit current. That is, NV NT Diode 1500 has abuilt-in current limit determined by the design of sub-component FETDiode 1505. FET diode examples are shown in the reference Baker, R. etal., “CMOS Circuit Design, Layout, and Simulation”, IEEE Press, 1998,pp. 165-171.

FIG. 21A illustrates an embodiment of a circuit 2100 in which stimuluscircuit 2110 applies voltage V to one terminal of resistor R. The otherterminal of resistor R is connected to terminal T1 of NV NT Diode 1200.Terminal T2 of NV NT Diode 1200 is connected to a common referencevoltage, ground for example. NV NT Diode 1200 is formed by a diode inseries with a NV NT Switch as described further above with respect toFIG. 12. The output of circuit 2100 is terminal T1 voltage V_(OUT).

FIG. 21B illustrates equivalent circuit embodiment 2110 for NV NT diode1200 in an ON state. Equivalent circuit 2110 corresponds to NV NT Switch600 in the ON state as illustrated in FIG. 6A. FIG. 21C illustrates I-Velectrical characteristics 2120 of nonvolatile nanotube diode 1200 inthe ON state. The NV NT diode 1200 turn-on voltage is approximately 0.4to 0.5 volts, for example. After turn-on, the slope of the I-V curvecorresponds to the ON resistance of NV NT switch 1210, where R_(ON-NT)is typically in the range of 10 k Ohms to 100 kOhms as illustrated inFIGS. 9A-9B.

FIG. 21D illustrates equivalent circuit embodiment 2130 of NV NT diode1200 in an OFF state. The equivalent circuit corresponds to NV NT Switch600′ in the OFF state as illustrated in FIG. 6B. FIG. 21E illustratesthe I-V electrical characteristics 2140 of nonvolatile nanotube diode1200 in the OFF state. I-V characteristic 2140 corresponds to R_(OFF-NT)of greater than 100 MOhm for some NV NT switches, and greater than 10GOhms for other NV NT switches illustrated in FIGS. 9A-9B.

In an exemplary read operation, referring to circuit 2100 in FIG. 21A,output voltage V_(OUT) will be a high voltage if NV NT Diode 1200 is ina high OFF resistance state; and output voltage V_(OUT) will be low ifNV NT Diode 1200 is in a low ON resistance state as illustrated in FIG.22. In this example, R is assumed to be much larger than the ONresistance of NV NT Diode 1200 and much smaller than the OFF resistanceof NV NT Diode 1200. Since the ON resistance of NV NT Diode 1200 may bein the range of 10 kOhm to 100 kOhm and the OFF resistance of NV NTDiode 1200 may be greater than 100 MOhm to 10 GOhms and higher asdescribed further above, then R may be chosen as 1 MOhm, for example.

In an exemplary read operation in which NV NT Diode 1200 is in an OFFstate, the OFF resistance of NV NT Diode 1200 is much greater thanresistance R and when applying read voltage waveforms 2200-1 illustratedin FIG. 22 to circuit 2100 results in a V_(OUT) transition from zero to2 volts when input V transitions from 0 to 2 volts. This is becauseresistance R of 1 M Ohm is much smaller than NV NT Diode 1200 resistanceof 100 MOhms to 10 GOhms or more.

In an exemplary read operation in which NV NT Diode 1200 is in an ONstate, the ON resistance of NV NT Diode 1200 is much less thanresistance R and when applying read voltage waveforms 2200-2 illustratedin FIG. 22 to circuit 2100 results in a V_(OUT) transition from zero to0.4-0.5 volts when input V transitions from 0 to 2 volts. This isbecause resistance R of 1 M Ohm is larger than the ON resistance of NVNT Diode 1200. The low voltage value of V_(OUT) is 0.4-0.5 volts becausethat is the forward voltage of NV NT Diode 1200. As explained furtherabove, the forward voltage occurs because diode 1205 is a sub-componentof NV NT Diode 1200 as explained further above with respect to FIGS. 12and 21A-21E.

FIG. 23A illustrates an embodiment of a circuit 2300 in which stimuluscircuit 2310 applies voltage V to one terminal of resistor R. The otherterminal of resistor R is connected to terminal T1 of NV NT Diode 1500.Terminal T2 of NV NT Diode 1500 is connected to a common referencevoltage, ground for example. NV NT Diode 1500 is formed by an FET diodein series with a NV NT Switch as described further above with respect toFIG. 15. The output of circuit 2300 is terminal T1 voltage V_(OUT).

In a read operation, referring to circuit 2300 in FIG. 23A, outputvoltage V_(OUT) will be a high voltage if NV NT Diode 1500 (NV NTFET-Diode 1500) is in a high OFF resistance state; and output voltageV_(OUT) will be low if NV NT Diode 1500 is in a low ON resistance stateas illustrated in FIG. 23B. In this example, R is assumed to be muchlarger than the ON resistance of NV NT Diode 1500 and much smaller thanthe OFF resistance of NV NT Diode 1500. Since the ON resistance of NV NTDiode 1500 may be in the range of 10 kOhm to 100 kOhm and the OFFresistance of NV NT Diode 1500 may be greater than 100 MOhm to 10 GOhmsand higher as described further above, then R may be chosen as 1 MOhm,for example.

In an exemplary read operation in which NV NT Diode 1500 is in an OFFstate, the OFF resistance of NV NT Diode 1500 is much greater thanresistance R and when applying read voltage waveforms 2300-1 illustratedin FIG. 23B to circuit 2300 results in a V_(OUT) transition from zero to2 volts when input V transitions from 0 to 2 volts. This is becauseresistance R of 1 M Ohm is much smaller than NV NT Diode 1500 resistanceof 100 MOhms to 10 GOhms or more.

In an exemplary read operation in which NV NT Diode 1500 is in an ONstate, the ON resistance of NV NT Diode 1500 is much less thanresistance R and when applying read voltage waveforms 2300-2 illustratedin FIG. 23B to circuit 2300 results in a V_(OUT) transition from zero to0.5 volts when input V transitions from 0 to 2 volts. This is becauseresistance R of 1 M Ohm is larger than the ON resistance of NV NT Diode1500. The low voltage value of V_(OUT) is 0.5 volt because that is theforward voltage of NV NT Diode 1500. As explained further above, theforward voltage occurs because FET diode 1505 is a sub-component of NVNT Diode 1500.

FIG. 24 illustrates an embodiment of a circuit 2400 in which NV NT Diode1200 includes a nonvolatile two terminal transfer device. Stimuluscircuit 2410 applies voltage V to one terminal of resistor R. The otherterminal of resistor R is connected to terminal T1 of NV NT Diode 1200.Terminal T2 of NV NT Diode 1200 is connected to one terminal of secondresistor R′; the other terminal of resistor R′ is connected to a commonreference voltage, ground for example. NV NT Diode 1200 is formed by adiode in series with a NV NT switch as described further above withrespect to FIG. 12. An equivalent circuit and I-V characteristics for NVNT diode 1200 is illustrated in FIGS. 21A-21E. The output of circuit2400 is terminal T2 voltage V′_(OUT).

In an exemplary signal transfer operation, referring to circuit 2400 inFIG. 24, output voltage V_(OUT) will be a low voltage if NV NT Diode1200 is in a high OFF resistance state; and output voltage V_(OUT) willbe high if NV NT Diode 1200 is in a low ON resistance state asillustrated in FIG. 25. In this example, R is assumed to be much largerthan the ON resistance of NV NT Diode 1200 and much smaller than the OFFresistance of NV NT Diode 1200. Since the ON resistance of NV NT Diode1200 may be in the range of 10 kOhm to 100 kOhm and the OFF resistanceof NV NT Diode 1200 may be greater than 100 MOhm to 10 GOhms and higheras described further above, then R may be chosen as 1 MOhm, for example.In this example, resistor R′ is assumed to be equal to resistor R.

In an exemplary signal transfer operation in which NV NT Diode 1200 isin an OFF state, the OFF resistance of NV NT Diode 1200 is much greaterthan resistance R and applying signal transfer voltage waveforms 2500-1illustrated in FIG. 25 to circuit 2400 results in a V_(OUT) remaining atapproximately zero volts when input V transitions from 0 to 2 volts.This is because resistance R of 1 M Ohm is much smaller than NV NT Diode1200 resistance of 100 MOhms to 10 GOhms or more and voltage V appearsacross NV NT Diode 1200; resistor R′ is also 1 M Ohm.

In an exemplary signal transfer operation in which NV NT Diode 1200 isin an ON state, the ON resistance of NV NT Diode 1200 is much less thanresistance R and applying read voltage waveforms 2300-2 illustrated inFIG. 25 to circuit 2400 results in voltage V dividing between two equalresistance values R and R′ of 1 M Ohm. V′_(OUT) transition from zero toapproximately 1 volt when input V transitions from 0 to 2 volts. This isbecause resistance R of 1 M Ohm is larger than the ON resistance of NVNT Diode 1200, and with resistance R′ also equal to 1 MOhm, signaltransfer circuit 2400 with NV NT Diode 1200 in the ON state behaves as a2:1 voltage divider.

Nonvolatile Memories Using Nonvolatile Nanotube Diode (NV NT Diode)Devices as Cells

A bit-selectable nonvolatile nanotube-based memory array describedfurther below includes a plurality of memory cells, each cell receivinga bit line and a word line. Each memory cell includes a selection diodewith anode and cathode terminals (nodes). Each cell further includes atwo terminal nonvolatile nanotube switch device, the state of whichmanifests the logical state of the cell. The combined diode andnonvolatile nanotube switch is referred to as a nonvolatile nanotubediode (NT NT Diode) as described further above. Each memory cell isformed using one nonvolatile nanotube diode. The state of thenonvolatile nanotube switch-portion of the nonvolatile nanotube diodemay be changed (cycled) between an ON resistance state and an OFFresistance state separated by at least one order of magnitude, buttypically separated by two to five orders of magnitude. There is nopractical limit to the number of times nonvolatile nanotube switches maybe cycled between ON and OFF states.

Each memory cell may be formed using a nonvolatile nanotube diode withan internal cathode-to-nonvolatile nanotube switch connection, or anonvolatile nanotube diode with an internal anode-to-nonvolatilenanotube switch connection, with a horizontal orientation, or with avertical (three dimensional) orientation to maximize density. In orderto further maximize density, memory arrays are integrated above supportcircuits and interconnections that are integrated in and on anunderlying semiconductor substrate.

Nonvolatile Memories Using NV NT Diode Devices with Cathode-to-NT SwitchConnection

In some embodiments, a nonvolatile nanotube diode (NV NT diode) is a twoterminal nonvolatile device formed by two series devices, a diode (e.g.,a two terminal Schottky or PN diode) in series with a two terminalnonvolatile nanotube switch (NV NT switch). Each of the two said seriesdevices has one shared series electrical connection. Acathode-to-nanotube NV NT diode has the cathode terminal electricallyconnected to one of said two nonvolatile nanotube switch terminals. SaidNV NT diode two terminal nonvolatile device has one available terminalconnected to the anode of the Schottky or PN diode and the secondavailable terminal connected to the free terminal of the NV NT switch. Aschematic of an embodiment of a cathode-to-NT nonvolatile nanotube diodeis illustrated in FIG. 12. PIN diodes, FET diodes, and other diode typesmay also be used.

In some embodiments, dense 3D memories may be formed using one NV NTdiode per cell. Embodiments of memories using NV NT diodes withcathode-to-NT connections are illustrated schematically and memoryoperation is described further below. 3-D cell structures areillustrated including fabrication methods. Cells with NV NT diodesformed with NV NT switches with both vertical and horizontalorientations are illustrated further below.

Nonvolatile Systems and Circuits, with Same

One embodiment of a nonvolatile memory 2600 is illustrated in FIG. 26A.Memory 2600 includes memory array 2610 having cells C00 through C33formed using nonvolatile nanotube diodes similar to nonvolatile nanotubediode 1200 (NV NT Diode 1200) having a diode-cathode-to-nonvolatilenanotube switch terminal connection such as that illustrated in FIG. 12.A diode similar to diode 1205 of NV NT Diode 1200 is used as a cellselect device and a nonvolatile storage switch similar to NV NT Switch1210 of NV NT Diode 1200 is used to store a nonvolatile ON (lowresistance) state or a nonvolatile OFF (high resistance) state. ON andOFF states represent nonvolatile logic “1” or “0” states, respectively.Note that logic “1” and logic “0” state assignments with respect to lowand high resistance states are arbitrary and may be reversed, forexample.

Nonvolatile memory 2600 illustrated in FIG. 26A includes memory array2610 having a matrix of NV NT Diode cells C00 through C33 similar to NVNT Diode 1200 as explained further above. Nonvolatile cell C00, as othercells in the array, includes one NV NT Diode referred to as NV NT DiodeC00 which is similar to NV NT Diode 1200 illustrated further above. Theanode of NV NT Diode C00 is connected to bit line BL0, and the otherterminal of NV NT Diode C00, a NV NT Switch terminal, is connected toword line WL0.

In the illustrated embodiment, memory array 2610 is a 4-word line by4-bit line 16 bit memory array that includes word lines WL0, WL1, WL2,and WL3 and bit lines BL0, BL1, BL2, and BL3. Word line driver circuits2630 connected to word lines WL0 through WL3 and selected by worddecoder and WL select logic 2620 provide stimulus during write 0, write1, and read operations. BL driver and sense circuits 2640 provide datamultiplexers (MUXs), BL drivers and sense amplifier/latches and areconnected to bit lines BL0 through BL3 and selected by bit decoder andBL select logic 2650 provide stimulus during write 0, write 1, and readoperation; that is receive data from memory array 2610 and transmit datato memory array 2610. Data in memory array 2610 is stored in anonvolatile state such that power (voltage) supply to memory 2600 may beremoved without loss of data. BL driver and sense circuits 2640 are alsoconnected to read/write buffer 2660. Read/write buffer 2660 transmitsdata from memory array 2610 to read/write buffer 2660 which in turntransmits this data off-chip. Read/write buffer 2660 also accepts datafrom off-chip and transmits this data to BL driver and sense circuits2640 that in turn transmit data to array 2610 for nonvolatile storage.Address buffer 2670 provides address location information.

For an exemplary write 0 operation along word line WL0, simultaneouslyerasing cells C00, C01, C02, and C03, data stored in cells C00-C03 mayoptionally be read prior to erase and data stored in corresponding senseamplifier/latches. Write 0 operations along word line WL0 proceeds withbit lines BL0, BL1, BL2, and B3 transitioning from zero to 5 volts, withbit line drivers controlled by corresponding BL drivers in BL driver andsense circuits 2640. Next, WL driver circuits 2630 drive word line WL0from 5 volts to zero volts thus forward biasing NV NT Diodes C00, C01,C02, and C03 that form cells C00, C01, C02, and C03, respectively. Awrite 0 voltage of approximately 4.5 volts (erase voltage 5 volts minusNV NT diode turn on voltage of less than 0.5 volts as illustrated inFIG. 21) results in a transition from an ON state to an OFF state for NVNT Diodes in an ON state; NV NT Diodes in an OFF state remain in an OFFstate. Thus after a write 0 operation along word line WL0, NV NT DiodesC00-C03 are all in an OFF state. Unselected word lines WL1, WL2, and WL3all remain unselected and at 5 volts, and nonvolatile data stored incorresponding cells remains unchanged.

Note that while FIG. 26A illustrates a 4×4 memory array 2610, the arraycan be made arbitrarily large (e.g., to form an ˜8 kB array), and theassociated electronics modified appropriately.

The exemplary write 0 and write 1 operations illustrated in FIG. 26B aredescribed with respect to write 0 (erase) voltages of 4.5 volts andwrite 1 (write) voltages of 3.5 volts applied across the two terminalsof NV NT switches. However, with further reduction in NV NT switchchannel length (below 20 nm), and/or improved nanotube element SWNTand/or MWNT materials, and/or improved device structures such NV NTswitches that include suspended regions as described further above,write 0 and write 1 voltages may be reduced to the 1 to 3 volt range, orother ranges, for example.

In this example, an exemplary write operation is preceded by a write 0operation as described further above. In other words, NV NT DiodesC00-C03 of respective corresponding cells C00-C03 begin the writeoperation in the OFF state. For an exemplary write 0 operation to cellC00 for example, in which a logic 0 state is to be stored, NV NT DiodeC00 is to remain in the logic 0 high resistance state. Therefore, bitline BL0 is held at zero volts by corresponding BL driver and sensecircuits 2640. Next, word line WL0 transitions from 4 volts to zerovolts, with stimulus from WL drivers 2630. NV NT Diode C00 remains backbiased during the write 0 operation and cell C00 remains in an OFF (highresistance) logic 0 state.

If NV NT Diode C00 is to transition from an OFF (high resistance state)to an ON (low resistance state) in a write 1 operation representing alogic 1, then bit line BL0 transitions from zero volts to 4 volts, withstimulus provided by corresponding BL drivers in BL driver and sensecircuits 2640. Next, word line WL0 transitions from 4 volts to zerovolts. A write 1 voltage of approximately 4 volts results in a voltageof 3.5 volts across the terminals of a corresponding NV NT switchsub-component of NV NT diode C00 (4 volts minus NV NT diode turn onvoltage of less than 0.5 volts as illustrated in FIG. 21) results in atransition from an OFF state to an ON state for NV NT Diode C00.

For an exemplary read operation, from cells C00-C03 for example, the bitline drivers in BL driver and sense circuits 2640 precharge bit linesBL0-BL3 to a high voltage such as a read voltage of 2 volts, forexample. The read bit line voltage is selected to be less than bothwrite 0 and write 1 voltages to ensure that stored logic states (bits)are not disturbed (changed) during a read operation. Word line drivercircuits 2630 drives word line WL0 from 2 volts to zero volts. If NV NTDiode C00 in cell C00 is in an OFF state (storing a logic 0) then bitlines BL0 is not discharged and remains at 2 volts. A correspondingsense amplifier/latch in BL driver and sense circuits 2640 stores alogic 0. However, if NV NT Diode C00 in cell C00 is in an ON state, thenbit line BL0 is discharged. A corresponding sense amplifier/latch in BLdriver and sense circuits 2640 detects the reduced voltage and latches alogic 1.

FIG. 26B illustrates examples of operational waveforms 2600′ that may beapplied to an embodiment of memory 2600 illustrated in FIG. 26A duringwrite 0, write 1, and read operations (or modes). A pre-write 0 readoperation may optionally be performed before a write 0 operation inorder to record cell states along a selected word line, such as wordline WL0, in corresponding latches. Cells C00, C01, C02, and C03 receivewrite 0 pulses (nearly) simultaneously. At the beginning of a write 0operation, bit lines BL0, BL1, BL2, and BL3 transition from zero to 5volts as illustrated by waveforms 2600′ in FIG. 26B. Next, word line WL0transitions from 5 volts to zero volts thereby forward-biasing NV NTDiodes C00-C03. Approximately 4.5 volts appears across the respective NVNT Switches in each of the NV NT Diodes because of a less than 0.5 voltforward-bias voltage drop. If the write 0 voltage of corresponding NV NTSwitch is 4.5 volts (or less), then NV NT Diodes transition from an ON(low resistance) state to an OFF (high resistance) state; NV NT Diodesin an OFF state remain in an OFF state. Thus after a write 0 operationalong word line WL0, NV NT Diodes C00-C03 are all in an OFF state.Unselected word lines WL1, WL2, and WL3 all remain unselected and at 5volts.

In this example, a write operation is preceded by a write 0 operation asdescribed further above with respect to FIG. 26A. In other words, forcells along word line WL0, NV NT Diodes C00-C03 are in an OFF state atthe beginning of the write operation. For exemplary write operationsillustrated by waveforms 2600′, NV NT Diodes C00 and C03 are to remainin the OFF state for a write 0 operation, and NV NT Diodes C01 and C02are to transition from an OFF state to an ON state in a write 1operation.

Therefore, at the beginning of the write cycle, bit lines BL0 and BL3remain at zero volts. Next, word line WL0 transitions from 4 volts tozero volts. NV NT Diodes C00 and C03 remain back biased during the write0 operation, and therefore NV NT Diodes remain in the OFF state storinga logic 0 state.

Continuing the exemplary write cycle, cells C01 and C02 transition froman OFF to an ON state. Bit lines BL1 and BL2 transition from zero to 4volts. Next, word line WL0 transitions from 4 volts to zero volts. NV NTDiodes C01 and C02 are forward biased during the write 1 operation andapproximately 3.5 volts appear across NV NT Switches corresponding to NVNT Diodes C01 and C02. NV NT Diodes C01 and C02 transition from an OFFto an ON state storing a logic 1 state.

For an exemplary read operation as illustrated by waveforms 2600′ inFIG. 26B, bit lines BL0, BL1, BL2, and BL3 are precharged to 2 volts,for example, and allowed to float. Then word line WL0 transitions from 2volts to zero volts. Word lines WL1, WL2, and WL3 remain at 2 volts. Forcells C00 and C03, bit line BL0 and BL3 voltage remains unchangedbecause NV NT Diodes C00 and C03 are in an OFF or high resistance stateand bit line BL0 and BL3 capacitance cannot discharge to ground (zerovolts). However, for cells C01 and C02, bit lines BL1 and BL2 dischargetoward zero volts because NV NT Diodes C01 and C02 are in an ON or lowresistance state and bit line capacitance for BL1 and BL2 can dischargetoward ground (zero volts). For BL1 and BL2, corresponding senseamplifier/latches typically detect bit line voltage reduction in the 100mV to 200 mV range, although this value may vary depending upon theparticular characteristics (design) of the sense/latch circuit.Corresponding sense amplifier/latches in BL driver and sense circuits2640 determine that BL1 and BL2 read voltages have changed and latch alogic 1 state corresponding to the ON state of NV NT Diodes C01 and C02that form cells C01 and C02. Corresponding sense amplifier/latches in BLdriver and sense circuits 2640 determine that BL0 and BL3 have notchanged and latch a logic 0 state corresponding to the OFF state of NVNT Diodes C00 and C03 forming cells C00 and C03.

An Overview of 3-Dimensional Cell Structure Methods of Fabrication ofNonvolatile Memory Cells Using NV NT Devices

Nonvolatile nanotube diodes 1200 and 1300 (NV NT Diodes 1200, 1300), andnonvolatile nanotube diodes formed with FET diodes, referred to as NV NTDiodes 1400, 1500, 1600, and 1700 or also as NV NT FET-Diodes 1400,1500, 1600, and 1700, may be used as cells and interconnected intoarrays to form nonvolatile nanotube random access memory systems. Sucharrays may also be used to fabricate nonvolatile array-based logic suchas PLAs, FPGAs, PLDs and other such logic devices.

FIG. 27A illustrates an overview of a method 2700 of fabricating someembodiments of the invention. While method 2700 is described furtherbelow with respect to nonvolatile nanotube diodes 1200 and 1300, method2700 is sufficient to cover the fabrication of many of the nonvolatilenanotube diodes described further above. These methods 2700 may also beused to form logic embodiments based on NV NT diodes arranged as logicarrays such as NAND and NOR arrays with logic support circuits (insteadof memory support circuits) as used in PLAs, FPGAs, and PLDs, forexample.

In general, methods 2710 fabricate support circuits and interconnectionsin and on a semiconductor substrate. This includes NFET and PFET deviceshaving drain, source, and gate that are interconnected to form memorysupport circuits such as, for example, circuits 2620, 2630, 2640, 2650,2660, and 2670 illustrated in FIG. 26A. Such structures and circuits maybe formed using known techniques that are not described in thisapplication. Methods 2710 can be used to form a base layer using knownmethods of fabrication in and on which nonvolatile nanotube diodecontrol devices and circuits are fabricated.

Methods 2720 fabricate an intermediate structure including a planarizedinsulator with interconnect means and nonvolatile nanotube arraystructures on the planarized insulator surface. Interconnect meansinclude vertically-oriented filled contacts, or studs, forinterconnecting memory support circuits in and on a semiconductorsubstrate below the planarized insulator with nonvolatile nanotube diodearrays above and on the planarized insulator surface.

Word lines and bit lines can be used in 3D array structures as describedfurther below to interconnect 3-D cells and form 3-D memories, and canbe approximately orthogonal in an X-Y plane approximately parallel tounderlying memory support circuits. Word line direction has beenarbitrarily assigned as along the X axis and bit line direction hasarbitrarily assigned as along the Y axis in figures illustrating 3Darray structures and 3D array structure methods of fabrication asdescribed further below. The Z axis, approximately orthogonal to the X-Yplane, indicates the vertical direction of 3D cell orientation, in“vertical cell” embodiments such as those described in greater detailbelow.

Methods 2750 use industry standard fabrication techniques to completefabrication of the semiconductor chip by adding additional wiring layersas needed, and passivating the chip and adding package interconnectmeans.

3-Dimensional Cell Structure of Nonvolatile Cells Using NV NT DevicesHaving Vertically Oriented Diodes and Vertically Oriented NT Switcheswith Cathode-to-NT Switch Connection

Once support circuits and interconnections in and on the semiconductorsubstrate are defined, methods can then be used to fabricate anonvolatile nanotube diode array such as that illustrated in crosssection 2800 above the support circuit and interconnect region asillustrated in FIG. 28A. FIG. 28A illustrates a cross section includingcells C00 and C01 in one of several possible embodiments.

Methods 2710 described further above can be used to define supportcircuits and interconnections 2801.

Next, methods 2730 illustrated in FIG. 27B deposit and planarizeinsulator 2803. Interconnect means through planar insulator 2803 (notshown in cross section 2800 but shown further below with respect tocross section 2800″ in FIG. 28C) may be used to connect metal arraylines in 3-D arrays to corresponding support circuits andinterconnections 2801. By way of example, bit line drivers in BL driverand sense circuits 2640 may be connected to bit line BL0 in array 2610of memory 2600 illustrated in FIG. 26A. At this point in the fabricationprocess, methods 2740 may be used to form a memory array on the surfaceof insulator 2803, interconnected with memory array support structure2805-1 illustrated in FIG. 28A.

Methods 2740 illustrated in FIG. 27B deposit and planarize metal,polysilicon, insulator, and nanotube elements to form nonvolatilenanotube diodes which, in this example, include multiple verticallyoriented diode and vertically oriented nonvolatile nanotube switchseries pairs. Individual cell outer dimensions are formed in a singleetch step, each cell having a single NV NT Diode defined by a singletrench etch step after layers, except the WL0 layer, have been depositedand planarized, in order to eliminate accumulation of individual layeralignment tolerances that would substantially increase cell area.Individual cell dimensions in the X direction are 1F (1 minimum feature)as illustrated in FIG. 28A, and also 1F in the Y direction (not shown)which is orthogonal to the X direction, with a periodicity in X and Ydirections of 2F. Hence, each cell occupies an area of approximately4F². The vertically-oriented (Z direction) NV NT switch element(nanotube element) placement at R in the X direction is parallel to thetrench-defined outer dimensions with R approximately equal to F/2 inthis example, where NV NT switch (nanotube element) separation distanceis controlled by self-aligned means described further below with respectto FIGS. 34A-34FF. Vertically-oriented NV NT switch element (nanotubeelement) placement in the Y direction is typically not critical andtypically does not require self-alignment means.

Vertically oriented nanotube element placement R at approximately F/2assumes nanotube film thickness that is much less than cell dimension F.For a 45 nm technology node, for example, a nanotube element in thethickness range of 0.5 nm to 10 nm, for example. Nanotube elements maybe formed using a single nanotube layer, or may be formed using multiplelayers. Such nanotube element layers may be deposited e.g., usingspin-on coating techniques or spray-on coating techniques, as describedin greater detail in the incorporated patent references. FIGS. 28A and28B 3-D memory array structure embodiments and corresponding exemplarymethods of fabrication illustrated with respect to FIGS. 34A-34FF show3D array structures assuming vertically oriented nanotube elementsplaced at R, with R approximately equal to F/2. Such elements include abottom contact, a sidewall contact, electrically separated by avertically oriented nanotube element channel length L_(SW-CH) asillustrated further below with respect to FIGS. 28A, 28B embodiments andcorresponding FIG. 34A-34FF exemplary methods of fabrication.

In one possible variation, vertically oriented nanotube elementsthickness may be too thick for placement at F/2 for cells with dimensionF. For example, for a cell dimension F of 35 nm, for example, and ananotube film thickness of 10-20 nm, placement of vertically orientednanotube elements may be at F/3 for example, to accommodate both thenanotube element and a protective insulator as illustrated further belowwith respect to FIG. 39. Vertically oriented nanotube element withlower, sidewall, and upper contacts may still be used.

In another possible variation, a nanotube element thickness may be equalto the overall cell dimension F. For example, for a cell dimension F of35 nm, a nanotube film thickness of 35 nm may be used. Or, for example,for a cell dimension F of 22 nm, a nanobube film thickness of 22 nm maybe used. In this case the nanotube element contact structure may bemodified such that the sidewall contact is eliminated and replaced bylower and upper contacts only as illustrated further below in FIG. 40.The thickness of the nanotube element need not be related in anyparticular way to the lateral cell dimension F.

In addition to the simultaneous definition of overall cell dimensionswithout multiple alignment steps, minimized memory cell size (area) alsorequires the self-aligned placement of device elements within saidmemory cell boundaries using sub-minimum dimensions, in this example,cell boundaries defined by isolation trenches. Cross sections 2800 and2800′ in FIGS. 28A and 28B, respectively, illustrate exemplarynonvolatile nanotube switches similar to cross section 750 illustratedin FIG. 7B, except that the nanotube channel element position R isself-aligned to isolation trenches that determine overall celldimensions. Also, lower level, sidewall, and upper level contacts areall self-aligned and fit within isolation trench boundaries.Self-aligned placement of device elements within defined boundaries maybe achieved by adapting sidewall spacer methods such as those disclosedin U.S. Pat. No. 4,256,514, the entire contents of which areincorporated herein by reference.

In some embodiments, methods fill trenches with an insulator and thenplanarize the surface. Then, methods deposit and pattern word lines onthe planarized surface.

The fabrication of vertically-oriented 3D cells proceeds as follows, insome embodiments. Referring to FIG. 28A, methods deposit a bit linewiring layer on the surface of insulator 2803 having a thickness of 50to 500 nm, for example, as described further below with respect to FIGS.34A-34FF. Methods etch the bit line wiring layer and define individualbit lines such as bit line 2810-1 (BL0) and 2810-2 (BL1). Bit lines suchas BL0 and BL1 are used as array wiring conductors and may also be usedas anode terminals of Schottky diodes. Alternatively, more optimumSchottky diode junctions 2818-1 and 2818-2 may be formed using metal orsilicide contacts 2815-1 and 2815-2 in contact with N polysiliconregions 2820-1 and 2820-2, while also forming ohmic contacts with bitlines 2810-1 and 2810-2 as described further below with respect to FIGS.34A-34FF. N polysilicon regions 2820-1 and 2820-2 may be doped witharsenic or phosphorus in the range of 10¹⁴ to 10¹⁷ dopant atoms/cm³ forexample, and may have a thickness range of 20 nm to 400 nm, for example.Contacts 2815-1 and 2815-2 may be in the thickness range of 10 nm to 500nm, for example.

In some embodiments, the electrical characteristics of Schottky (and PN)diodes may be improved (low leakage, for example) by controlling thematerial properties of polysilicon, for example polysilicon depositedand patterned to form polysilicon regions 2820-1 and 2820-2. Polysiliconregions may have relatively large or relatively small grain boundarysize that are determined by methods used in the semiconductor regions.SOI deposition methods used in the semiconductor industry may be usedthat result in polysilicon regions that are single crystalline (nolonger polysilicon), or nearly single crystalline, for furtherelectrical property enhancement such as low diode leakage currents.

Examples of contact and conductors materials are elemental metals suchas, Al, Au, W, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, as wellas metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides, oxides, or silicides such as RuN,RuO, TiN, TaN, CoSi_(x) and TiSi_(x). Insulators may be SiO₂, SiN_(x),Al₂O₃, BeO, polyimide, Mylar or other suitable insulating material.

In some cases conductors such as Al, Au, W, Cu, Mo, Ti, and others maybe used as both contact and conductors materials as well as anodes forSchottky Diodes, in which case separate optional Schottky anodescontacts such as 2815-1 and 2815-2 are not required and may be omitted.However, in other cases, optimizing anode material for lower forwardvoltage drop and lower diode leakage is advantageous. Schottky diodeanode materials may include Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo,Na, Ni, Os, Pb, Pd, Pt, Rb, Ru, Ti, W, Zn and other elemental metals.Also, silicides such as CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂,and ZrSi₂ may be used. Schottky diodes formed using such metals andsilicides are illustrated in the reference by NG, K. K. “Complete Guideto Semiconductor Devices”, Second Edition, John Wiley & Sons, 2002m pp.31-41, the entire contents of which are incorporated herein byreference.

Next, having completed Schottky diode select devices, methods form N+polysilicon regions 2825-1 and 2825-2 to contact N polysilicon regions2820-1 and 2820-2, respectively, and also to form contact regions forohmic contacts to contacts 2830-1 and 2830-2. N+ polysilicon istypically doped with arsenic or phosphorous to 10²⁰ dopant atoms/cm³,for example, and has a thickness of 20 to 400 nm, for example.

Next, methods form a nonvolatile nanotube switch in each cell having oneterminal common with cathode contacts 2830-1 and 2830-2 for example. Inorder to enhance the density of cells C00 and C01, the nanotube elementsillustrated in FIG. 28A may be at least partially vertically oriented asillustrated in FIG. 7. Vertically oriented nanotube switches aredescribed in greater detail in the incorporated patent references.Vertically oriented sidewalls including insulating and contact regionsare formed prior to forming vertically oriented nanotube elements 2845-1and 2845-2. Vertically oriented sidewalls are formed using self alignedmethods at position R approximately equal to F/2. However, similar selfaligned methods of fabrication may be used to place the verticallyoriented sidewalls at any location, such as F/3, F/4, or any otherdesired location.

Methods of forming nanotube elements 2845-1 and 2845-2 can include firstforming insulators 2835-1 and 2835-2 and sidewall contacts 2840-1 and2840-2, in contact with corresponding insulators 2835-1 and 2835-2, bydirectionally etching an opening through both metal and insulatorregions to form vertical sidewalls. The thickness of insulators 2835-1and 2835-2 determine the nanotube element channel length as illustratedin FIG. 28A. Insulator 2835-1 and 2835-2 may range from less than 5 nmto greater than 250 nm. Vertical sidewalls of insulators 2835-1 and2835-2 and sidewall contacts 2840-1 and 2840-2 are self aligned withrespect to trench sidewalls that are etched later in the process usingmethods of fabrication described further below with respect to FIGS.34A-34FF.

Next, methods form conformal nanotube elements 2845-1 and 2845-2 asdescribed in greater detail in the incorporated patent references.

Then, methods form protective conformal insulator 2850-1 and 2850-2 onthe surface of conformal nanotube elements 2845-1 and 2845-2,respectively.

Next, methods form an opening having an X dimension of approximately Fand methods fill that opening with a conductor material forming upperlevel contacts 2865-1 and 2865-2 in contact with sidewall contacts2840-1 and 2840-2, respectively. Methods to form upper level contacts2865-1 and 2865-2 may be similar to methods disclosed in U.S. Pat. No.4,944,836 and described further below with respect to FIGS. 34A-34FF.

Contacts 2865-1 and 2865-2 provide a conductive path between sidewallcontacts 2840-1 and 2840-2, respectively, and word line 2871 (WL0) to beformed after completing the formation of cells C00 and C01.

Next, prior to the formation of word line 2871 (WL0), cell C00 and cellC01 dimensions can be defined by a trench etch through all layers incell structure 2800, down to the top surface of insulator 2803.

Next, methods fill trench regions with an insulator 2860 and planarizethe structure just prior to word line 2871 (WL0) deposition.

Then, methods deposit and pattern word line 2871 (WL0).

Nonvolatile nanotube diode 2880 schematic superimposed on cross section2800 in FIG. 28A is an equivalent circuit that corresponds tononvolatile nanotube diode 1200 in FIG. 12, one in each of cells C00 andC01. Cells C00 and C01 illustrated in cross section 2800 in FIG. 28Acorrespond to corresponding cells C00 and C01 shown schematically inmemory array 2610 in FIG. 26A, and bit lines BL0 and BL1 and word lineWL0 correspond to array lines illustrated schematically in memory array2610.

Cross sectional view 2800′ illustrated in FIG. 28B shows embodiments ofmemory array cells C00′ and C01′ that are similar to memory array cellsC00 and C01 illustrated in FIG. 28A, except that NV NT Diodes C00′ andNV NT Diodes C01′ formed in corresponding cells C00′ and C01′ include aPN diodes having PN diode junctions 2819-1 and 2819-2 instead of aSchottky diodes having a Schottky diode junctions 2818-1 and 2818-2.

P polysilicon regions 2817-1 and 2817-2 form a diode-anode and Npolysilicon regions 2820-1′ and 2820-2′ form a diode cathode thattogether (combined) form PN diodes with PN diode junctions 2819-1 and2819-2. P polysilicon regions 2817-1 and 2817-2 also form ohmic ornear-ohmic contacts with bit lines 2810-1′ (BL0) and 2810-2′ (BL1),respectively. N polysilicon regions 2820-1′ and 2820-2′ also form ohmiccontact regions with N+ polysilicon regions 2825-1 and 2825-2. Otherstructures of cells C00′ and C01′ are similar to those illustrated anddescribed with respect to cells C00 and C01, respectively.

Memory array support structure 2805-2 illustrated in FIG. 28B includessupport circuits and interconnections 2801′ and planarized insulator2803′ which are similar to memory support structure 2801 illustrated inFIG. 28A except for adjustments that may be required to accommodatememory cells having PN diode select means instead of Schottky diodeselect means.

3-Dimensional Cell Structure of Nonvolatile Cells Using NV NT DevicesHaving Vertically Oriented Diodes and Horizontally Oriented NT Switcheswith Cathode-to-NT Switch Connection

Methods 2720 illustrated in FIG. 27B can be used to deposit andplanarize metal, polysilicon, insulator, and nanotube elements to formnonvolatile nanotube diodes with multiple vertically oriented diode andhorizontally oriented nonvolatile nanotube switch series pairs asillustrated by cross section 2800″ in FIG. 28C.

Cell C00″ in the embodiment of FIG. 28C is formed on memory arraysupport structure 2805-3, which includes support circuits andinterconnections 2801″ and planarized insulator 2803″. Support circuitsand interconnections 2801″ is similar to support circuits andinterconnections 2801 and planarized insulator 2803″ is similar toplanarized insulator 2803 in FIG. 28A, except for adjustments needed toaccommodate differences in cell C00″ with respect to cell C00. Also,cross section 2800″ includes filled-via contact (stud) 2807 thatinterconnects bit line 2810″ (BL0) with support circuits andinterconnections 2801″ circuits as illustrated in cross section 2800″ ofFIG. 28C. For example, filled via contact (stud) 2807 may connect bitline BL0 illustrated schematically in FIG. 26A with BL driver and sensecircuits 2640.

Individual outer cell dimensions can be formed in a single etch step,each cell having a single NV NT Diode defined by a single trench etchstep after layers, except the WL0 layer, have been deposited andplanarized, in order to eliminate accumulation of individual layeralignment tolerances that may substantially increase cell area.Individual cell dimensions in the X direction are 2-3 F (1F is minimumfeature) as illustrated in FIG. 28C because horizontal nonvolatilenanotube switch orientation typically require more area than nonvolatilenanotube switches having a vertical orientation such as thoseillustrated in FIGS. 28A and 28B. Minimum Y direction (orthogonal to theX direction, not shown), dimensions of 1F in the Y direction arepossible. Using cell periodicity in the X direction of 3-4F andperiodicity in the Y direction of 2F, in some embodiments each celloccupies an area in the range of 6-8F² or larger. After trench fill withan insulator followed by planarization, word lines such as word line2875 are deposited and patterned.

Cross section 2800″ illustrated in FIG. 28C shows an embodiment of amemory array cell C00″ that is similar to the memory array cellembodiment C00 illustrated in FIG. 28A, except that NV NT diode C00″forming cell C00″ includes a horizontally oriented nonvolatile nanotubeswitch instead of the vertically oriented nonvolatile nanotube switchillustrated in cross section 2800 in FIG. 28A.

In FIG. 28C, cross section 2800″ cell C00″ select Schottky diodeincludes Schottky diode junction 2821 corresponding to Schottky diodejunction 2818-1 in cross section 2800 of FIG. 28A. Schottky diodejunction 2821 is formed by bit line 2810″ (BL0) forming the anode and Npolysilicon 2820″ forming the cathode. An optional additional metalcontact such as metal contact 2815-1 is not shown in cross section 2800″but may be added. N+ polysilicon region 2825″ is added for contact to Npolysilicon region 2820″ and corresponds to N+ polysilicon region 2825-1in FIG. 28A.

Methods can be used fabricate a nonvolatile nanotube switch having ahorizontal (instead of a vertical) orientation and having one side ofthe nonvolatile nanotube switch in electrical (not physical) contactwith N+ polysilicon region 2825″ and the other side of the nonvolatilenanotube switch in electrical (not physical) contact with word line2875.

First, methods deposit insulator 2830″ and contact 2835″. Then methodsform an opening through both contact 2835″ and insulator 2830″ to exposethe surface of N+ polysilicon region 2825″.

Next, methods deposit a conformal insulating layer on the top, sidewall,and bottom of the underlying opening. Then, methods directional etch theconformal insulating layer thereby forming sidewall spacer 2840, whosethickness determines the channel length L_(SW-CH) of the nonvolatilenanotube switch in cell C00″. Cross section 2800″ shows two L_(SW-CH)regions. These two L_(SW-CH) regions are electrically in parallel (notshown by cross section 2800″). Exemplary methods of fabrication aredescribed further below with respect to FIGS. 35A-S.

Next, methods fill the opening with contact metal, followed byplanarization, to form contact 2845, which forms an Ohmic contact to N+polysilicon region 2825″ and is isolated from contact 2835″ regions bysidewall spacer 2840.

Next, methods deposit nanotube element 2850 on and in physical andelectrical contact with contact 2845, spacers 2840, and sidewall contact2835″. The separation between contact 2845 and contact 2835″, which isformed by the thickness of sidewall spacer 2840, determines thenonvolatile nanotube switch channel length L_(SW-CH). Nanotube element2850 may optionally be patterned as illustrated in FIG. 28C, or may bepatterned as part of a later trench etch that determines final cell C00″dimensions. Exemplary methods of fabrication are described further belowwith respect to FIGS. 35A-35S.

Next, methods deposit insulator 2855.

Next, methods etch insulator 2855 forming an opening. Then, methods etch(remove) the exposed portion of nanotube element 2850, e.g., asdescribed in greater detail in the incorporated patent references.

Next, the opening is filled with contact metal 2865. Methods formcontact metal 2865 by metal deposition followed by planarization.Contact 2865 physically and electrically contacts both contact 2835″ andnanotube element 2850.

Next, methods etch a trench through all layers, stopping on the surfaceof insulator 2803″, thereby defining the dimensions of cell C00″

Next, methods deposit and planarize an insulating layer forminginsulator 2874.

Then, methods deposit and pattern word line 2875 (WL0) completing cellC00″. Exemplary methods of fabrication are described further below withrespect to FIGS. 35A-35S.

Nonvolatile nanotube diode embodiment 2885 in FIG. 28C is an equivalentcircuit that corresponds to nonvolatile nanotube diode 1200 in FIG. 12in cell C00″. Cell C00″ corresponds to corresponding cell C00 shownschematically in the embodiment of the memory array 2610 illustrated inFIG. 26A, and bit line BL0 and word line WL0 correspond to array linesillustrated schematically in memory array 2610.

Nonvolatile Memories Using NV NT Diode Devices with Anode-to-NT SwitchConnection

In some embodiments, a nonvolatile nanotube diode (NV NT diode) is a twoterminal nonvolatile device formed by two series devices, a diode (e.g.,a two terminal Schottky or PN diode) in series with a two terminalnonvolatile nanotube switch (NV NT switch). Each of the two said seriesdevices has one shared series electrical connection. Ananode-to-nanotube NV NT diode has the anode terminal electricallyconnected to one of said two nonvolatile nanotube switch terminals. SaidNV NT diode two terminal nonvolatile device has one available terminalconnected to the cathode of the Schottky or PN diode and the secondavailable terminal connected to the free terminal of the NV NT switch. Aschematic of an anode-to-NT nonvolatile nanotube diode is illustrated inFIG. 13. PIN diodes, FET diodes, and other diode types may also be used.

In some embodiments, dense 3D memories may be formed using one NV NTdiode per cell. Embodiments of memories using NV NT diodes withanode-to-NT connections are illustrated schematically and memoryoperation is described further below. Exemplary 3-D cell structures areillustrated including fabrication methods. Exemplary cells with NV NTdiodes formed with NV NT switches with vertically orientated switchesare illustrated further below.

Nonvolatile Systems and Circuits, with Same

One embodiment of a nonvolatile memory 2900 is illustrated in FIG. 29A.Memory 2900 includes memory array 2910 having cells C00 through C33formed using nonvolatile nanotube diodes similar to nonvolatile nanotubediode 1300 (NV NT Diode 1300) formed using diode-anode-to-nonvolatilenanotube switch terminal connection such as that illustrated in FIG. 13.A diode similar to diode 1305 of NV NT Diode 1300 is used as a cellselect device and a nonvolatile storage switch similar to NV NT Switch1310 of NV NT Diode 1300 is used to store a nonvolatile ON (lowresistance) state or a nonvolatile OFF (high resistance) state. ON andOFF states represent nonvolatile logic “1” or “0” states, respectively.Note that logic “1” and logic “0” state assignments with respect to lowand high resistance states are arbitrary and may be reversed, forexample.

Nonvolatile memory 2900 illustrated in FIG. 29A includes memory array2910 having a matrix of NV NT Diode cells C00 through C33 similar to NVNT Diode 1300 as explained further above. Nonvolatile cell C00, as othercells in the array, includes one NV NT Diode referred to as NV NT DiodeC00 which is similar to NV NT Diode 1300 illustrated further above. Thecathode of NV NT Diode C00 is connected to word line WL0, and the otherterminal of NV NT Diode C00, a NV NT Switch terminal, is connected tobit line BL0.

In the illustrated embodiment, memory array 2910 is a 4-word line by4-bit line 16 bit memory array that includes word lines WL0, WL1, WL2,and WL3 and bit lines BL0, BL1, BL2, and BL3. Word line driver circuits2930 connected to word lines WL0 through WL3 and selected by worddecoder and WL select logic 2920 provide stimulus during write 0, write1, and read operations. BL driver and sense circuits 2940 that providedata MUXs, BL drivers and sense amplifier/latches are connected to bitlines BL0 through BL3 and selected by bit decoder and BL select logic2950 provide stimulus during write 0, write 1, and read operation; thatis receive data from memory array 2910 and transmit data to memory array2910. Data in memory array 2910 is stored in a nonvolatile state suchthat power (voltage) supply to memory 2900 may be removed without lossof data. BL driver and sense circuits 2940 are also connected toread/write buffer 2960. Read/write buffer 2960 transmits data frommemory array 2910 to read/write buffer 2960 which in turn transmits thisdata off-chip. Read/write buffer 2960 also accepts data from off-chipand transmits this data to BL driver and sense circuits 2940 that inturn transmit data to array 2910 for nonvolatile storage. Address buffer2970 provides address location information.

Note that while FIG. 29A illustrates a 4×4 memory array 2910, the arraycan be made arbitrarily large (e.g., to form an 8 kB array), and theassociated electronics modified appropriately.

For an exemplary write 0 operation along word line WL0, simultaneouslyerasing cells C00, C01, C02, and C03, data stored in cells C00-C03 mayoptionally be read prior to erase and data stored in corresponding senseamplifier/latches. Write 0 operation along word line WL0 proceeds withbit lines BL0, BL1, BL2, and B3 transitioning from zero to 5 volts, withbit line drivers controlled by corresponding BL drivers in BL driver andsense circuits 2940. Next, WL driver circuits 2930 drive word line WL0from 5 volts to zero volts thus forward biasing NV NT Diodes C00, C01,C02, and C03 that form cells C00, C01, C02, and C03, respectively. Awrite 0 voltage of approximately 4.5 volts (write 0 voltage 5 voltsminus NV NT diode turn on voltage of less than 0.5 volts) results in atransition from an ON state to an OFF state for NV NT Diodes in an ONstate; NV NT Diodes in an OFF state remain in an OFF state. Thus after awrite 0 operation along word line WL0, NV NT Diodes C00-C03 are all inan OFF state. Unselected word lines WL1, WL2, and WL3 all remainunselected and at 5 volts, and nonvolatile data stored in correspondingcells remains unchanged.

In this example, a write operation is preceded by a write 0 operation asdescribed further above. In other words, NV NT Diodes C00-C03 ofrespective corresponding cells C00-C03 begin the write operation in theOFF state. For an exemplary write 0 operation to cell C00 for example,in which a logic 0 state is to be stored, NV NT Diode C00 is to remainin the logic 0 high resistance state. Therefore, bit line BL0 is held atzero volts by corresponding BL driver and sense circuits 2940. Next,word line WL0 transitions from 4 volts to zero volts, with stimulus fromWL drivers 2930. NV NT Diode C00 remains back biased during the write 0operation and cell C00 remains in an OFF (high resistance) logic 0state.

If NV NT Diode C00 is to transition from an OFF (high resistance state)to an ON (low resistance state) in a write 1 operation representing alogic 1, then bit line BL0 transitions from zero volts to 4 volts, withstimulus provided by corresponding BL drivers in BL driver and sensecircuits 2940. Next, word line WL0 transitions from 4 volts to zerovolts. A write 1 voltage of approximately 4 volts results in a voltageof 3.5 volts across the terminals of a corresponding NV NT switchsub-component of NV NT diode C00 (4 volts minus NV NT diode turn onvoltage of less than 0.5 volts) results in a transition from an OFFstate to an ON state for NV NT Diode C00.

For an exemplary read operation, from cells C00-C03 for example, the bitline drivers in BL driver and sense circuits 2940 precharge bit linesBL0-BL3 to a high voltage such as a read voltage of 2 volts, forexample. The read bit line voltage is selected to be less than bothwrite 0 and write 1 voltages to ensure that stored logic states (bits)are not disturbed (changed) during a read operation. Word line drivercircuits 2930 drives word line WL0 from 2 volts to zero volts. If NV NTDiode C00 in cell C00 is in an OFF state (storing a logic 0), then bitlines BL0 is not discharged and remains at 2 volts. A correspondingsense amplifier/latch in BL driver and sense circuits 2940 stores alogic 0. However, if NV NT Diode C00 in cell C00 is in an ON state, thenbit line BL0 is discharged. A corresponding sense amplifier/latch in BLdriver and sense circuits 2940 detects the reduced voltage and latches alogic 1.

FIG. 29B illustrates examples of operational waveforms 2900′ that may beapplied to the embodiment of memory 2900 illustrated in FIG. 29A duringwrite 0, write 1, and read operations (or modes). A pre-write 0 readoperation may optionally be performed before a write 0 operation inorder to record cell states along a selected word line, such as wordline WL0, in corresponding latches. Cells C00, C01, C02, and C03 receivewrite 0 pulses (nearly) simultaneously. At the beginning of an write 0operation, bit lines BL0, BL1, BL2, and BL3 transition from zero to 5volts as illustrated by waveforms 2900′ in FIG. 29B. Next, word line WL0transitions from 5 volts to zero volts thereby forward-biasing NV NTDiodes C00-C03. Approximately 4.5 volts appears across the respective NVNT Switches in each of the NV NT Diodes because of a less than 0.5 voltforward-bias voltage drop. If the write 0 voltage of corresponding NV NTSwitch is 4.5 volts (or less), then NV NT Diodes transition from an ON(low resistance) state to an OFF (high resistance) state; NV NT Diodesin an OFF state remain in an OFF state. Thus after a write 0 operationalong word line WL0, NV NT Diodes C00-C03 are all in an OFF state.Unselected word lines WL1, WL2, and WL3 all remain unselected and at 5volts.

In this example, a write operation is preceded by a write 0 operation asdescribed further above with respect to FIG. 29A. In other words, forcells along word line WL0, NV NT Diodes C00-C03 are in an OFF state atthe beginning of the write operation. For exemplary write operationsillustrated by waveforms 2900′, NV NT Diodes C00 and C03 are to remainin the OFF state for a write 0 operation, and NV NT Diodes C01 and C02are to transition from an OFF state to an ON state in a write 1operation.

Therefore, at the beginning of the write (program) cycle, bit lines BL0and BL3 remain at zero volts. Next, word line WL0 transitions from 4volts to zero volts. NV NT Diodes C00 and C03 remain back biased duringthe write 0 operation, and therefore NV NT Diodes remain in the OFFstate storing a logic 0 state.

Continuing the exemplary write cycle, cells C01 and C02 transition froman OFF to an ON state. Bit lines BL1 and BL2 transition from zero to 4volts. Next, word line WL0 transitions from 4 volts to zero volts. NV NTDiodes C01 and C02 are forward biased during the write 1 operation andapproximately 3.5 volts appear across NV NT Switches corresponding to NVNT Diodes C01 and C02. NV NT Diodes C01 and C02 transition from an OFFto an ON state storing a logic 1 state.

For an exemplary read operation as illustrated by waveforms 2900′ inFIG. 29B, bit lines BL0, BL1, BL2, and BL3 are precharged to 2 volts,for example, and allowed to float. Then word line WL0 transitions from 2volts to zero volts. Word lines WL1, WL2, and WL3 remain at 2 volts. Forcells C00 and C03, bit line BL0 and BL3 voltage remains unchangedbecause NV NT Diodes C00 and C03 are in an OFF or high resistance stateand bit line BL0 and BL3 capacitance cannot discharge to ground (zerovolts). However, for cells C01 and C02, bit lines BL1 and BL2 dischargetoward zero volts because NV NT Diodes C01 and C02 are in an ON or lowresistance state and bit line capacitance for BL1 and BL2 can dischargetoward ground (zero volts). For BL1 and BL2, corresponding senseamplifier/latches typically detect bit line voltage reduction in the 100mV to 200 mV range, although this value may vary depending upon theparticular characteristics (design) of the sense/latch circuit.Corresponding sense amplifier/latches in BL driver and sense circuits2940 determine that BL1 and BL2 read voltages have changed and latch alogic 1 state corresponding to the ON state of NV NT Diodes C01 and C02that form cells C01 and C02. Corresponding sense amplifier/latches in BLdriver and sense circuits 2940 determine that BL0 and BL3 have notchanged and latch a logic 0 state corresponding to the OFF state of NVNT Diodes C00 and C03 forming cells C00 and C03.

3-Dimensional Cell Structure of Nonvolatile Cells Using NV NT DevicesHaving Vertically Oriented Diodes and Vertically Oriented NT Switcheswith Anode-to-NT Switch Connection

FIG. 30A illustrates an exemplary method 3000 of fabricating embodimentsof NV NT diodes having vertically oriented NT switches. While method3000 is described further below with respect to nonvolatile nanotubediodes 1300 such as illustrated in FIG. 13, method 3000 is sufficient tocover the fabrication of many of the nonvolatile nanotube diodeembodiments described further above. Note also that although methods3000 are described below in terms of memory embodiments, methods 3000may also be used to form logic embodiments based on NV NT diodesarranged as logic arrays such as NAND and NOR arrays with logic supportcircuits as used in PLAs, FPGAs, and PLDs, for example.

In general, methods 3010 fabricate support circuits and interconnectionsin and/or on a semiconductor substrate. This includes NFET and PFETdevices having drain, source, and gate that are interconnected to formmemory support circuits such as, for example, circuits 2920, 2930, 2940,2950, 2960, and 2970 illustrated in FIG. 29A. Such structures andcircuits may be formed using known techniques that are not described inthis application. Methods 3010 can be used to form a base layer usingknown methods of fabrication in and on which nonvolatile nanotube diodecontrol devices and circuits are fabricated.

Methods 3020 fabricate an intermediate structure including a planarizedinsulator with interconnect means and nonvolatile nanotube arraystructures on the planarized insulator surface. Interconnect meansinclude vertically-oriented filled contacts, or studs, forinterconnecting memory support circuits in and on a semiconductorsubstrate below the planarized insulator with nonvolatile nanotube diodearrays above and on the planarized insulator surface.

Word lines and bit lines can be used in 3D array structures as describedfurther below to interconnect 3-D cells and form 3-D memories, and canbe approximately orthogonal in an X-Y plane approximately parallel tounderlying memory support circuits. Word line direction has beenarbitrarily assigned as along the X axis and bit line direction hasarbitrarily assigned as along the Y axis in figures illustratingexemplary 3D array structures and 3D array structure methods offabrication as described further below. The Z axis, approximatelyorthogonal to the X-Y plane, indicates the direction of 3D cellorientation.

Methods 3050 use industry standard fabrication techniques to completefabrication of the semiconductor chip by adding additional wiring layersas needed, and passivating the chip and adding package interconnectmeans.

Once support circuits and interconnections in and on the semiconductorsubstrate are defined, methods then fabricate nonvolatile nanotube diodearray such as that illustrated in cross section 3100 above the supportcircuit and interconnect region as illustrated in FIG. 31A. FIG. 31Aillustrates a cross section including cells C00 and C10 in one ofseveral possible embodiments.

Methods 3010 described further above are used to define support circuitsand interconnections 3101.

Next, methods 3030 illustrated in FIG. 30B deposit and planarizeinsulator 3103. Interconnect means through planar insulator 3103 (notshown in cross section 3100 but shown further above with respect tocross section 2800″ in FIG. 28C) may be used to connect wiring metallines in arrays to corresponding support circuits and interconnections3101. By way of example, word line drivers in WL drivers 2930 may beconnected to word line WL0 in array 2910 of memory 2900 illustrated inFIG. 29A. At this point in the fabrication process, methods may be usedto form a memory array on the surface of insulator 3103, interconnectedwith of memory array support structure 3105-1 illustrated in FIG. 31A.

Methods 3040 illustrated in FIG. 30B deposit and planarize metal,polysilicon, insulator, and nanotube elements to form nonvolatilenanotube diodes which, in this example, include multiple verticallyoriented diode and vertically oriented nonvolatile nanotube switchseries pairs. Fabrication methods are described in more detail furtherbelow with respect to FIG. 36A-36FF. Individual cell outer dimensionscan be formed in a single etch step, each cell having a single NV NTDiode defined by a single trench etch step after layers, except the BL0layer, have been deposited and planarized, in order to eliminateaccumulation of individual layer alignment tolerances that maysubstantially increase cell area. Individual cell dimensions in the Ydirection are 1F (1 minimum feature) as illustrated in FIG. 31A, andalso 1F in the X direction (not shown) which is orthogonal to the Ydirection, with a periodicity in X and Y direction of 2F. Hence, eachcell occupies an area of at least approximately 4F². Nonvolatilenanotube diodes that form each cell are oriented in the Z (vertical)direction.

In addition to the simultaneous definition of overall cell dimensionswithout multiple alignment steps, in some embodiments reduced memorycell size (area) also requires the self-aligned placement of deviceelements within said memory cell boundaries.

Methods fill trenches with an insulator and then methods planarize thesurface. Methods deposit and pattern bit lines on the planarizedsurface.

The fabrication of some embodiments of vertically-oriented 3D cellsproceeds as follows. Methods deposit a word line wiring layer on thesurface of insulator 3103 having a thickness of 50 to 500 nm, forexample, as described further below with respect to FIGS. 36A-36FF.Methods etch the word line wiring layer and define individual word linessuch as word lines 3110-1 (WL0) and 3110-2 (WL1). Word lines such as3110-1 and 3110-2 are used as array wiring conductors and may also beused as individual cell contacts to N+ polysilicon regions 3120-1 and3120-2. N+ polysilicon regions 3120-1 and 3120-2 contact cathodes formedby N polysilicon regions 3125-1 and 3125-2. Schottky diode junctions3133-1 and 3133-2 may be formed using metal or silicide 3130-1 and3130-2 regions in contact with N Polysilicon regions 3125-1 and 3125-2.N Polysilicon regions 3125-1 and 3125-2 may be doped with arsenic orphosphorus in the range of 10¹⁴ to 10¹⁷ dopant atoms/cm³ for example,and may have a thickness range of 20 nm to 400 nm, for example. N+polysilicon is typically doped with arsenic or phosphorous to 10²⁰dopant atoms/cm³, for example, and has a thickness of 20 to 400 nm, forexample.

Examples of contact and conductors materials are elemental metals suchas, Al, Au, W, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, as wellas metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides, oxides, or silicides such as RuN,RuO, TiN, TaN, CoSi_(x) and TiSi_(x). Insulators may be SiO₂, SiN_(x),Al₂O₃, BeO, polyimide, Mylar or other suitable insulating material.

In some cases conductors such as Al, Au, W, Cu, Mo, Ti, and others maybe used as anodes 3130-1 and 3130-2 for Schottky Diodes. However, inother cases, optimizing anode 3130-1 and 3130-2 material for lowerforward voltage drop and lower diode leakage is advantageous. Schottkydiode anode materials may include Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir,Mg, Mo, Na, Ni, Os, Pb, Pd, Pt, Rb, Ru, Ti, W, Zn and other elementalmetals. Also, silicides such as CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂,WSi₂, and ZrSi₂ may be used. Schottky diodes formed using such metalsand silicides are illustrated in the reference by NG, K. K. “CompleteGuide to Semiconductor Devices”, Second Edition, John Wiley & Sons,2002m pp. 31-41, the entire contents of which are incorporated herein byreference.

At this point in the exemplary process Schottky diode select deviceshave been formed. Next, one nonvolatile nanotube switch is formed ineach cell having one terminal common with anode metal 3130-1 and 3130-2for example. In order to enhance the density of cells C00 and C10, thenanotube element in the corresponding nonvolatile nanotube switch isvertically oriented as illustrated in FIG. 31A with correspondingnanoswitch 700 illustrated in FIG. 7. Vertically oriented nanotubeswitches are described in greater detail in the incorporated patentreferences. Vertically oriented sidewalls including insulating andcontact regions are formed prior to forming vertically oriented nanotubeelements 3145-1 and 3145-2. Vertically oriented sidewalls are formed atR using self aligned methods, where R is approximately equal to F/2 inthis example, however, similar self aligned methods of fabrication maybe used to place the vertically oriented sidewalls at any location, suchas F/3, F/4, or any other desired location.

Methods of forming nanotube elements 3145-1 and 3145-2 include firstforming insulators 3135-1 and 3135-2 and contacts 3140-1 and 3140-2, incontact with corresponding insulators 3135-1 and 3135-2, bydirectionally etching an opening through both metal and insulatorregions to form vertical sidewalls. Vertical sidewalls of insulators3135-1 and 3135-2 and sidewall contacts 3140-1 and 3140-2 are selfaligned with respect to trench sidewalls that are etched later in theprocess using methods of fabrication described further below withrespect to FIGS. 36A-36FF. The thickness of insulators 3135-1 and 3135-2determine the channel length L_(SW-CH) as illustrated in FIG. 31A.Insulators 3135-1 and 3135-2 may range from less than 5 nm to greaterthan 250 nm, for example.

Next, methods form conformal nanotube elements 3145-1 and 3145-2 asdescribed in greater detail in the incorporated patent references.

Then, methods form protective conformal insulator 3150-1 and 3150-2 onthe surface of conformal nanotube elements 3145-1 and 3145-2,respectively.

Next, methods fill the opening with an insulating material and methodsplanarize the surface exposing the top surface of sidewall contacts3140-1 and 3140-2.

Then, methods form contacts 3165-1 and 3165-2. Contacts 3165-1 andcontacts 3165-2 provide a conductive path between sidewall contacts3140-1 and 3140-2, respectively, and bit line 3171 (BL0) to be formedafter completing the formation of cells C00 and C10. Contacts 3165-1 and3165-2 correspond to the dimensions of a sacrificial layer used as atrench-etch masking layer of minimum dimension F prior to contacts3165-1 and 3165-2 formation, as described further below with respect toFIG. 36A-36FF, that is self aligned to NV NT switch elements 3145-1 and3145.

Then, methods etch trench regions, fill trenches with an insulator, andthen planarize the surface to form insulator 3160 prior to contacts3165-1 and 3165-2 formation described further below with respect to FIG.36A-36FF.

Then, methods deposit and pattern bit line 3171 (BL0).

Nonvolatile nanotube diode 3190 schematic superimposed on cross section3100 in FIG. 31A is an equivalent circuit that corresponds tononvolatile nanotube diode 1300 in FIG. 13, one in each of cell C00 andC10. Cells C00 and C10 illustrated in cross section 3100 in FIG. 31Acorrespond to corresponding cells C00 and C10 shown schematically inmemory array 2910 in FIG. 29A, and word lines WL0 and WL1 and bit lineBL0 correspond to array lines illustrated schematically in memory array2910.

Cross section 3100′ illustrated in FIG. 31B shows embodiments of memoryarray cells C00′ and C10′ that are similar to embodiments of memoryarray cells C00 and C10 illustrated in FIG. 31A, except that NV NTDiodes C00′ and NV NT Diodes C10′ formed in corresponding cells C00′ andC10′ include a PN diodes having PN diode junctions 3128-1 and 3128-2instead of a Schottky diodes having a Schottky diode junctions 3133-1and 3133-2.

P polysilicon regions 3127-1 and 3127-2 form an anode and N polysiliconregions 3125-1′ and 3125-2′ form a cathode that together form PN diodeswith PN diode junctions 3128-1 and 3128-2. P polysilicon regions 3127-1and 3127-2 also form ohmic or near-ohmic contacts with contact 3130-1′and 3130-2′. N polysilicon regions 3125-1′ and 3125-2′ also form ohmiccontact regions with corresponding N+ polysilicon regions. Otherstructures of cells C00′ and C10′ are similar to those illustrated anddescribed with respect to cells C00 and C10, respectively.

Memory array support structure 3105 of the embodiment illustrated inFIG. 31B includes support circuits and interconnections 3101′ andplanarized insulator 3103′ which are similar to memory support structure3101 illustrated in FIG. 31A except for adjustments that may be requiredto accommodate memory cells having PN diode select means instead ofSchottky diode select means.

Nonvolatile nanotube diode 3190′ is an equivalent circuit thatcorresponds to nonvolatile nanotube diode 1300 in FIG. 13, one in eachof cell C00′ and C10′. Cells C00′ and C10′ correspond to correspondingcells C00 and C10 shown schematically in memory array 2910 in FIG. 29A,and word lines WL0 and WL1 and bit line BL0 correspond to array linesillustrated schematically in memory array 2910.

Cross section 3100″ illustrated in FIG. 31C shows embodiments of memoryarray cells C00″ and C10″ that are similar to the embodiments of memoryarray cells C00 and C10 illustrated in FIG. 31A, except that NV NTDiodes C00″ and NV NT Diodes C10″ formed in corresponding cells C00″ andC101″ include diode junctions 3147-1 and 3147-2 including both PN diodeand Schottky diode junctions in parallel.

P-type semiconductor nanotube elements, a subset of NT elements 3145-1″and 3145-2″, in physical and electrical contact with N polysiliconregions 3125-1″ and 3125-2″ form a PN diode-anode and N polysiliconregions 3125-1″ and 3125-2″ form a cathode that together form PN diodeshaving PN diodes as part of combined PN and Schottky diode junctions3147-1 and 3147-2. Metallic type nanotube elements, also a subset of NTelements 3145-1″ and 3145-2″, in physical and electrical contact with Npolysilicon regions 3125-1″ and 3125-2″, form a Schottky diode-anode andN polysilicon regions 3125-1″ and 3125-2″ form a cathode for Schottkydiodes having Schottky diode junctions as part of combined PN andSchottky diode junctions 3147-1 and 3147-2. Therefore, combined PN andSchottky diode junctions 3147-1 and 3147-2 are composed of PN-typediodes and Schottky-type diodes in parallel and are formed by nanotubeelements 3145-1″ and 3145-2″ in contact with N polysilicon regions3125-1″ and 3125-2″, respectively.

N polysilicon regions 3125-1″ and 3125-2″ also form ohmic contactregions with corresponding N+ polysilicon regions 3120-1″ and 3120-2″,respectively. Nanotube element 3145-1″ and 3145-2″ are also in physicaland electrical contact with sidewall contacts 3140-1″ and 3140-2″.Sidewall contacts 3140-1″ and 3140-2″ are in contact with upper levelcontacts 3165-1″ and 3165-2″, respectively, which are in contact withbit line bit line 3171″ (BL0). Formation of upper level contacts isbriefly described further above with respect to FIG. 31A and in moredetail further below with respect to FIGS. 36A-36FF. Other structures ofcells C00″ and C10″ are similar to those illustrated and described withrespect to cells C00 and C10, respectively.

Memory array support structure 3105-3 illustrated in the embodiment ofFIG. 31C includes support circuits and interconnections 3101″ andplanarized insulator 3103″ which are similar to memory support structure3101 and planarized insulator 3103 illustrated in FIG. 31A except foradjustments that may be required to accommodate memory cells having PNdiode select means and Schottky diode select means in parallel.

Nonvolatile nanotube diode 3190″ is an equivalent circuit thatcorresponds to nonvolatile nanotube diode 1300 in FIG. 13, one in eachof cell C00″ and C10″. Cells C00″ and C10″ illustrated in cross section3100″ in the embodiment of FIG. 31C correspond to corresponding cellsC00 and C10 shown schematically in memory array 2910 in the embodimentof FIG. 29A, and word lines WL0 and WL1 and bit line BL0 correspond toarray lines illustrated schematically in memory array 2910.

Nonvolatile Memories Using NV NT Diode Device Stacks with BothAnode-to-NT Switch Connections and Cathode-to-NT Switch Connections

FIG. 32 illustrates an exemplary method 3200 of fabricating embodimentshaving two memory arrays stacked one above the other and on aninsulating layer above support circuits formed below the insulatinglayer and stacked arrays, and with communications means through theinsulating layer. While method 3200 is described further below withrespect to nonvolatile nanotube diodes 1200 and 1300, method 3200 issufficient to cover the fabrication of many of the embodiments ofnonvolatile nanotube diodes described further above. Note also thatalthough methods 3200 are described in terms of 3D memory embodiments,methods 3200 may also be used to form 3D logic embodiments based on NVNT diodes arranged as logic arrays such as NAND and NOR arrays withlogic support circuits (instead of memory support circuits) as used inPLAs, FPGAs, and PLDs, for example.

FIG. 33A illustrates a 3D perspective drawing 3300 that includes anembodiment having a two-high stack of three dimensional arrays, a lowerarray 3302 and an upper array 3304. Lower array 3302 includesnonvolatile nanotube diode cells C00, C01, C10, and C11. Upper array3304 includes nonvolatile nanotube diode cells C02, C12, C03, and C13.Word lines WL0 and WL1 are oriented along the X direction and bit linesBL0, BL1, BL2, and BL3 are oriented along the Y direction and areapproximately orthogonal to word lines WL1 and WL2. Nanotube elementchannel length L_(SW-CH) and channel width W_(SW-CH) are shown in 3Dperspective drawing 3300. Cross sections of embodiments that can be usedas cells C00, C01, C02 and C03 are illustrated further below in FIG. 33Band FIG. 33C; and embodiments that can be used as cells C00, C02, C12,and C10 are illustrated further below in FIG. 33B′.

In general, methods 3210 fabricate support circuits and interconnectionsin and/or on a semiconductor substrate. This includes NFET and PFETdevices having drain, source, and gate that can be interconnected toform memory (or logic) support (or select) circuits. Such structures andcircuits may be formed using known techniques that are not described inthis application. Methods 3210 are used to form a support circuits andinterconnections 3301 layer as part of cross section 3305 illustrated inFIG. 33B and cross section 3305′ illustrated in FIG. 33B′ using knownmethods of fabrication in and on which nonvolatile nanotube diodecontrol and circuits are fabricated. Support circuits andinterconnections 3301 are similar to support circuits andinterconnections 2801 and 3101 described further above, for example, butare modified to accommodate two stacked memory arrays. Note that whiletwo-high stacked memory arrays are illustrated in FIGS. 33A-33D, morethan two-high 3D array stacks may be formed (fabricated), including butnot limited to 4-high and 8 high stacks for example.

Next, methods 3210 are also used to fabricate an intermediate structureincluding a planarized insulator with interconnect means and nonvolatilenanotube array structures on the planarized insulator surface such asinsulator 3303 illustrated in cross section 3305 in FIG. 33B andcorresponding cross section 3305′ in FIG. 33B′. Interconnect meansinclude vertically-oriented filled contacts, or studs, forinterconnecting memory support circuits in and on a semiconductorsubstrate below the planarized insulator with nonvolatile nanotube diodearrays above and on the planarized insulator surface. Planarizedinsulator 3303 is formed using methods similar to methods 2730illustrated in FIG. 27B in which methods deposit and planarize insulator3303. Interconnect means through planar insulator 3303 (not shown incross section 3300) similar to contact 2807 illustrated in FIG. 28C maybe used to connect array lines in first memory array 3310 and secondmemory array 3320 to corresponding support circuits and interconnections3301 as described further below. Support circuits and interconnections3301 and insulator 3303 form memory array support structure 3305-1.

Next, methods 3220, similar to methods 2740, are used to fabricate afirst memory array 3310 using diode cathode-to-nanotube switches basedon a nonvolatile nanotube diode array similar to a nonvolatile nanotubediode array cross section 2800 illustrated in FIG. 28A and correspondingmethods of fabrication described further below with respect to FIGS.34A-34FF.

Next, methods 3230 similar to methods 3040 illustrated in FIG. 30B,fabricate a second memory array 3320 on the planar surface of firstmemory array 3310, but using diode anode-to-nanotube switches based on anonvolatile nanotube diode array similar to a nonvolatile nanotube diodearray cross section 3100 illustrated in FIG. 31A and correspondingmethods of fabrication described further below with respect to FIGS.36A-36FF.

FIG. 33B illustrates cross section 3305 including first memory array3310 and second memory array 3320, with both arrays sharing word line3330 in common, according to some embodiments. Word lines such as 3330can be defined (etched) during trench etch that defines memory array(cells) when forming array 3320. Cross section 3305 illustrates combinedfirst memory array 3310 and second memory array 3320 in the word line,or X direction, with shared word line 3330 (WL0), four bit lines BL0,BL1, BL2, and BL3, and corresponding cells C00, C01, C02, and C03. Thearray periodicity in the X direction is 2F, where F is a minimumdimension for a technology node (generation).

FIG. 33B′ illustrates cross section 3305′ including first memory array3310′ and second memory array 3320′ with both arrays sharing word lines3330′ and 3332 in common, according to some embodiments. Word line 3330′is a cross sectional view of word line 3330. Word lines such as 3330′and 3332 can be defined (etched) during a trench etch that definesmemory array (cells) when forming array 3320′. Cross section 3305′illustrates combined first memory array 3310′ and second memory array3320′ in the bit line, or Y direction, with shared word lines 3330′(WL0) and 3332 (WL1), two bit lines BL0 and BL2, and corresponding cellsC00, C10, C02, and C12. The array periodicity in the Y direction is 2F,where F is a minimum dimension for a technology node (generation).

The memory array cell area of 1 bit for array 3310 can be down to 4F²because of the 2F periodicity in the X and Y directions. The memoryarray cell area of 1 bit for array 3320 can be down to 4F² because ofthe 2F periodicity in the X and Y directions. Because memory arrays 3320and 3310 are stacked, the memory array cell area per bit can be down to2F². If four memory arrays (not shown) are stacked, then the memoryarray cell area per bit can be down to 1F².

Referring again to FIG. 32, methods 3240 using industry standardfabrication techniques complete fabrication of the semiconductor chip byadding additional wiring layers as needed, and passivating the chip andadding package interconnect means.

Cross section 3305 illustrated in FIG. 33B shows stacking of firstmemory array 3310 and second memory array 3320 with bit locationsaligned in the vertical (Z) direction, according to some embodiments,however there may be interconnection and/or fabrication advantages tooffsetting stacked memory arrays. FIG. 33C illustrates an embodimenthaving a cross section 3350″ similar to cross section 3305 illustratedin FIG. 33B in which second memory array 3320″ is translated by one celllocation (a half-periodicity) relative to cells in first memory array3310″ and sharing word line 3330″. Support circuits and interconnections3301′ and insulator 3303′ form memory array support structure 3305-2which is similar to memory array support structure 3305-1 illustrated inFIG. 33B.

In operation, the four stacked cells illustrated in FIG. 33B correspondto cell C00 and C01 cathode-to-nanotube cells illustrated schematicallyin memory array 2610 forming memory array 3310, and C02 and C03anode-to-nanotube cells illustrated schematically in memory array 2910forming memory array 3320. All four cells share common word line WL0 inmemory array cross section 3300. Cells C00, C01, C02, and C03 are alsoshown in 3D perspective drawing 3300 illustrated in FIG. 33A. Memoryarray 3305 is approximately 2× denser on a per bit basis than memoryarrays such as illustrated by cathode-to-NT cross section 2800illustrated in FIG. 28A or anode-to-NT cross section 3100 illustrated inFIG. 31A for example. Additional word lines and bit lines (not shown)may be added to form a large memory array in the megabit and gigabitrange. Word line WL0 and bit lines BL0, BL1, BL2, and BL3 operation isdescribed further below in terms of waveforms 3375 illustrated in FIG.33D with word line WL0 selected.

For an exemplary write 0 operation along word line WL0, simultaneouslyerasing cells C00, C01, C02, and C03, data stored in cells C00-C03 mayoptionally be read prior to erase and data stored in corresponding senseamplifier/latches. Write 0 operation along word line WL0 proceeds withbit lines BL0, BL1, BL2, and B3 transitioning from zero to 5 volts, withbit line voltages controlled by corresponding BL drivers. Next, WLdriver circuits drive word line WL0 from 5 volts to zero volts thusforward biasing NV NT Diodes C00, C01, C02, and C03 that form cells C00,C01, C02, and C03, respectively. A write 0 voltage of approximately 4.5volts (erase voltage 5 volts minus NV NT diode turn on voltage of lessthan 0.5 volts as illustrated in FIGS. 21A-21E) results in a transitionfrom an ON state to an OFF state for NV NT Diodes in an ON state; NV NTDiodes in an OFF state remain in an OFF state. Thus after a write 0operation along word line WL0, NV NT Diodes C00-C03 are all in an OFFstate. Unselected word lines WL1, WL2, and WL3 (not shown in FIG. 33B)remain unselected and at 5 volts, and nonvolatile data stored incorresponding cells remains unchanged.

In this example, a write operation is preceded by a write 0 operation asdescribed further above. In other words, NV NT Diodes C00-C03 ofrespective corresponding cells C00-C03 begin the write operation in theOFF state. For an exemplary write 0 operation to cells C00 and C03 forexample, in which a logic 0 state is to be stored, NV NT Diodes C00 andC03 are to remain in the logic 0 high resistance state. Therefore, bitlines BL0 and BL3 are held at zero volts by corresponding BL driver andsense circuits. Next, word line WL0 transitions from 4 volts to zerovolts, with stimulus from corresponding WL drivers. NV NT Diodes C00 andC03 remain back biased during the write 0 operation and cells C00 andC03 remain in an OFF (high resistance) logic 0 state.

If NV NT Diodes C01 and C02 are to transition from an OFF (highresistance state) to an ON (low resistance state) in a write 1 operationrepresenting a logic 1, then bit lines BL1 and BL2 transition from zerovolts to 4 volts, with stimulus provided by corresponding BL drivers.Next, word line WL0 transitions from 4 volts to zero volts. A write 1voltage of approximately 4 volts results in a voltage of 3.5 voltsacross the terminals of corresponding NV NT switch sub-components of NVNT diode C01 and C02 (4 volts minus NV NT diode turn on voltage of lessthan 0.5 volts as illustrated in FIG. 21) and result in a transitionfrom an OFF state to an ON state for NV NT Diodes C01 and C02.

For an exemplary read operation, from cells C00-C03 for example,corresponding bit line drivers in corresponding BL driver and sensecircuits precharge bit lines BL0-BL3 to a high voltage such as a readvoltage of 2 volts, for example. The read bit line voltage is selectedto be less than both write 0 and write 1 voltages to ensure that storedlogic states (bits) are not disturbed (changed) during a read operation.Word line drivers drive word line WL0 from 2 volts to zero volts. NV NTDiodes C00 and C03 in corresponding cells C01 and C03 are in an OFFstate (storing a logic 0) and bit lines BL0 and BL3 are not dischargedand remains at 2 volts. Corresponding sense amplifier/latches storecorresponding logic 0 states. However, since NV NT Diode C01 and C02 incorresponding cells C01 and C02 are in an ON state, then bit lines BL1and BL2 are discharged. Corresponding sense amplifier/latches detect areduced voltage and latches store corresponding logic 1 states.

Note that the memory array illustrated in cross section 3350″ of FIG.33C can be operated similarly to memory array illustrated in crosssection 3305 described further above with respect to FIG. 33B.

Methods of Fabricating Nonvolatile Memories Using Nonvolatile NanotubeDiode (NV NT Diode) Devices as Cells

Exemplary methods of fabricating embodiments of 3-dimensional cellstructures of nonvolatile cells using NV NT devices having verticallyoriented diodes and vertically oriented NV NT switches withcathode-to-NT switch connections such as illustrated by cross section2800 illustrated in FIG. 28A and cross section 2800′ illustrated in FIG.28B are described further below with respect to FIGS. 34A-34FF.

Exemplary methods of fabricating embodiments of 3-dimensional cellstructure of nonvolatile cells using NV NT Devices having verticallyoriented diodes and horizontally oriented NV NT switches withcathode-to-NT switch connections such as illustrated by cross section2800″ illustrated in FIG. 28C are described further below with respectto FIGS. 35A-35S.

Exemplary methods of fabricating 3-dimensional cell structureembodiments of nonvolatile cells using NV NT devices having verticallyoriented diodes and vertically oriented NV NT switches with anode-to-NTswitch connections such as illustrated by cross section 3100 illustratedin FIG. 31A, cross section 3100′ illustrated 31B, and cross section3100″ illustrated in FIG. 31C are described further below with respectto FIGS. 36A-FF.

Exemplary methods of fabrication of embodiments of stacked arrays basedon 3-dimensional cell structures of nonvolatile cells using NV NTDevices having vertically oriented diodes and vertically oriented NV NTswitches using both cathode-to-NT Switch and anode-to-NT switchconnected cell types, such as those shown in cross section 3300illustrated in FIG. 33A, cross section 3300′ illustrated in FIG. 33A′,and cross section 3300′ illustrated in FIG. 33B, are a combination ofmethods of fabrication described further below with respect to FIGS.34A-FF and 36A-FF.

Methods of Fabricating Nonvolatile Memories Using NV NT Diode Deviceswith Cathode-to-NT Switch Connection

Methods 2700 illustrated in FIGS. 27A and 27B may be used to fabricateembodiments of memories using NV NT diode devices with cathode-to-NTswitch connections for vertically oriented NV NT switches such as thoseshown in cross section 2800 illustrated in FIG. 28A and cross section2800′ illustrated in FIG. 28B as described further below with respect toFIGS. 34A-34FF. Structures such as cross section 2800 and 2800′ may beused to fabricate, e.g., memory 2600 illustrated schematically in FIG.26A.

Methods of fabricating cross sections 2800 and 2800′ typically requirecritical alignments in X direction process steps. There are no criticalalignments in the Y direction because in this example distance betweentrenches determines the width of the nanotube element. However, thewidth of the nanotube element may be formed to be less than thetrench-to-trench spacing by using methods similar to those describedfurther below with respect to the X direction. In the X direction,critical alignment requirements are eliminated by using methods thatform self-aligned internal cell vertical sidewalls that define verticalnanotube channel element location, vertical channel element length(L_(SW) _(—) _(CH)), and form nanotube channel element contacts withrespect to trench sidewalls that are etched later in the process todefine outer cell dimensions using methods of fabrication describedfurther below with respect to FIGS. 34A-34FF. In this example, NV NTdiode cell structures occupy a minimum dimension F in the X and Ydirections, where F is a minimum photolithographic dimension. In thisexample, the internal cell vertical sidewall is positioned (by selfalignment techniques) at approximately R distance from trench sidewallsthat are separated by distance F and that define outer cell dimensionsas illustrated further below with respect to FIGS. 34A-34FF. FIGS.34A-34FF is illustrated with a spacing R of approximately F/2. However,methods using self alignment techniques described further below withrespect to FIGS. 34A-34FF may position a vertical sidewall at anylocation R within the cell region of width F using R values of F/4, F/3,F/2, 3F/4, etc for example.

Methods 2700 illustrated in FIGS. 27A and 27B may also be used tofabricate embodiments memories using NV NT diode devices withcathode-to-NT switch connections for horizontally oriented NV NTswitches such as those shown in cross section 2800″ illustrated in FIG.28C as described further below with respect to FIGS. 35A-35S. Structuressuch as cross section 2800″ also may be used to fabricate memory, e.g.,memory 2600 illustrated schematically in FIG. 26A.

Methods of Fabricating 3-Dimensional Cell Structure of Nonvolatile CellsUsing NV NT Devices Having Vertically Oriented Diodes and VerticallyOriented NT Switches with Cathode-to-NT Switch Connection

Methods 2710 illustrated in FIG. 27A can be used to define supportcircuits and interconnects similar to those described with respect tomemory 2600 illustrated in FIG. 26A as described further above. Methods2710 apply known semiconductor industry techniques design andfabrication techniques to fabricated support circuits andinterconnections 3401 in and/or on a semiconductor substrate asillustrated in FIG. 34A. Support circuits and interconnections 3401include FET devices in a semiconductor substrate and interconnectionssuch as vias and wiring above a semiconductor substrate.

Next, methods 2730 illustrated in FIG. 27B deposit and planarizeinsulator 3403 on the surface of support circuits and interconnections3401 layer. Interconnect means through planar insulator 3403, not shownin FIG. 34A, are shown further below with respect to FIGS. 35A-35S. Thecombination of support circuits and interconnections 3401 and planarizedinsulator 3403 is referred to as memory support structure 3405 asillustrated in FIG. 34A.

Next, methods deposit a conductor layer 3410 on the planarized surfaceof insulator 3403 as illustrated in FIG. 34A, typically 50 to 500 nmthick, using known industry methods. Examples of conductors layermaterials are elemental metals such as, Al, Au, W, Cu, Mo, Pd, Ni, Ru,Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu,TiPd, PbIn, and TiW, other suitable conductors, or conductive nitrides,oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).In some cases materials such as those used in conductor layer 3410 mayalso be used as anodes for Schottky diodes, in which case a separatelayer such as contact layer 3415 used to form anodes of Schottky diodesis not required and may be omitted from methods of fabrication.

Next, methods deposit a an optional conductive Schottky anode contactlayer 3415 having a thickness range of 10 to 500 nm, for example, on thesurface of conductor layer 3410. Anode contact layer 3415 may usesimilar materials to those used in forming conductor layer 3410 (orcontact layer 3415 may be omitted entirely and conductor layer 3410 maybe used to form a Schottky anode), or anode contact layer 3415 materialmay be chosen to optimize anode material for enhanced Schottky diodeproperties such lower forward voltage drop and/or lower diode leakage.Anode contact layer 3415 may include Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir,Mg, Mo, Na, Ni, Os, Pb, Pd, Pt, Rb, Ru, Ti, W, Zn and other elementalmetals. Also, silicides such as CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂,WSi₂, and ZrSi₂ may be used.

Next, methods deposit an N polysilicon layer 3420 of thickness 10 nm to500 nm on the surface of anode contact layer 3415. N polysilicon layer3420 may be doped with arsenic or phosphorus in the range of 10¹⁴ to10¹⁷ dopant atoms/cm³, for example. N polysilicon layer 3420 may be usedto form cathodes of Schottky diodes. In addition to doping levels, thepolysilicon crystalline size (or grain structure) of N Polysilicon layer3420 may also be controlled by known industry methods of deposition.Also, known industry SOI methods of deposition may be used that resultin polysilicon regions that are single crystalline (no longerpolysilicon), or nearly single crystalline.

Next, having completed memory support structure 3405, then depositedconductor layer 3410 which may be used as an array wiring layer, andthen completed the deposition of Schottky diode forming layers 3415 and3420, methods deposit N+ polysilicon layer 3425 on the surface of Npolysilicon layer 3420 as illustrated in FIG. 34A in order to form anohmic contact layer. N+ polysilicon layer 3425 is typically doped witharsenic or phosphorous to 10²⁰ dopant atoms/cm³, for example, and has athickness of 20 to 400 nm, for example.

At this point in the process, remaining methods may be used to fabricateNV NT diode using Schottky diode-based cathode-to-NT switch structuressuch as those illustrated in FIG. 28A. However, as described furtherabove with respect to FIG. 28B for example, NV NT diodes may be formedusing PN diodes instead of Schottky diodes. Therefore, alternatively, aPN diode alternative fabrication method is illustrated in FIG. 34A′.

Methods 2700 described further above, and with respect to FIG. 34A, mayalso be used to describe the fabrication of FIG. 34A′. Support circuitsand interconnections 3401′ illustrated in FIG. 34A′ correspond tosupport circuits and interconnections 3401 illustrated in FIG. 34A,except for possible small changes that may be introduced in individualcircuits to accommodate differences in diode characteristics such asturn-on voltage, for example, between Schottky diodes and PN diodes.

Next, methods deposit planarized insulator 3403′ on the surface ofsupport circuits and interconnections 3401′ as illustrated in FIG. 34A′.Planarized insulator 3403′ corresponds to planarized insulator 3403except for possible small changes that may be introduced in insulator3403′ to accommodate differences in diode characteristics. Memorysupport structure 3405′ is therefore similar to support structures 3405except for small changes that may be introduced in support circuits andinterconnections 3401′ and planarized insulator 3403′ as describedfurther above with respect to FIG. 34A′.

Next, methods deposit conductor layer 3410′ in contact with the surfaceof planarized insulator 3403′ as illustrated in FIG. 34A′ which issimilar in thickness and materials to conductor layer 3410 describedfurther above with respect to FIG. 34A.

Next, methods deposit a P polysilicon layer 3417 of thickness 10 nm to500 nm on the surface of conductor layer 3410′ as illustrated in FIG.34A′. P polysilicon layer 3417 may be doped with boron in the range of10¹⁴ to 10¹⁷ dopant atoms/cm³, for example. P polysilicon layer 3417 maybe used to form anodes of PN diodes. In addition to doping levels, thepolysilicon crystalline size of P Polysilicon layer 3417 may also becontrolled by known industry methods of deposition. Also, known industrySOI methods of deposition may be used that result in polysilicon regionsthat are single crystalline (no longer polysilicon), or nearly singlecrystalline.

Next, methods deposit an N polysilicon layer 3420′ of thickness 10 nm to500 nm on the surface of P polysilicon layer 3417 that may be used toform cathodes of PN diodes. N polysilicon layer 3420′ may be doped witharsenic or phosphorus in the range of 10¹⁴ to 10¹⁷ dopant atoms/cm³, forexample. In addition to doping levels, the polysilicon crystalline size(grain structure) of N Polysilicon layer 3420′ may also be controlled byknown industry methods of deposition. Also, known industry SOI methodsof deposition may be used that result in polysilicon regions that aresingle crystalline (no longer polysilicon), or nearly singlecrystalline.

Next, having completed memory support structure 3405′, then depositedconductor layer 3410′ which may be used as an array wiring layer, andthen completed the deposition PN diode forming layers 3417 and 3420′, N+polysilicon layer 3425′ is deposited on N polysilicon layer 3420′ inorder to form an ohmic contact layer as illustrated in FIG. 34A′. N+polysilicon layer 3425′ is typically doped with arsenic or phosphorousto 10²⁰ dopant atoms/cm³, for example, and has a thickness of 20 to 400nm, for example.

Descriptions of methods of fabrication continue with respect toSchottky-diode based structures described with respect to FIG. 34A toform NV NT diode cell structures corresponding to cross section 2800illustrated in FIG. 28A. However, these methods of fabrication may alsobe applied to the PN diode-based structures described with respect toFIG. 34A′ to form NV NT diode cell structures corresponding to crosssection 2800′ illustrated in FIG. 28B.

At this point in the fabrication process, methods deposit contact layer3430 on the surface of N+ polysilicon layer 3425 as illustrated in FIG.34B. Contact layer 3430 may be 10 to 500 nm in thickness, for example.Contact layer 3430 may be formed using Al, Au, W, Cu, Mo, Pd, Ni, Ru,Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu,TiPd, PbIn, and TiW, other suitable conductors, or conductive nitrides,oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x),for example.

Next, methods deposit an insulator layer 3435 on contact layer 3430 asillustrated in FIG. 34B. The thickness of insulator layer 3435 may bewell controlled and in some embodiments can be used to determine thechannel length of vertically oriented nonvolatile nanotube switches asillustrated further below with respect to FIG. 34I. The thickness ofinsulator layer 3435 may vary in thickness from less than 5 nm togreater than 250 nm, for example. Insulator 3435 may be formed from anyknown insulator material in the CMOS industry, or packaging industry,for example such as SiO₂, SiN, Al₂O₃, BeO, polyimide, PSG(phosphosilicate glass), photoresist, PVDF (polyvinylidene fluoride),sputtered glass, epoxy glass, and other dielectric materials andcombinations of dielectric materials such as PVDF capped with an Al₂O₃layer, for example. U.S. patent application Ser. No. 11/280,786 includessome examples of various dielectric materials.

Next, methods deposit contact layer 3440 on insulator layer 3435 asillustrated in FIG. 34B. Contact layer 3440 may be in the range of 10 to500 nm thick, for example, and may be formed using various conductormaterials similar to materials described with respect to contact 3430described further above.

Next methods deposit sacrificial layer 3441 on contact layer 3440 asillustrated in FIG. 34C. Sacrificial layer 3441 may be in the range of10 to 500 nm thick, for example, and be formed using conductor,semiconductor, or insulator materials such as materials describedfurther above with respect to contact layer 3430, semiconductor layers3420 and 3425, and insulator layer 3435.

Next, methods deposit and pattern a masking layer such as masking layer3442 deposited on the top surface of sacrificial layer 3441 asillustrated in FIG. 34C using known industry methods. The mask openingmay be aligned to alignment marks in planar insulating layer 3403 forexample; the alignment is not critical.

Then, methods directionally etch sacrificial layer 3441 to form anopening of dimension D_(OPEN-1) in the X direction through sacrificiallayer 3441 stopping at the surface of contact layer 3440 using knownindustry methods as illustrated in FIG. 34D. Two memory cells thatinclude vertical nanotube channel elements self aligned and positionedwith respect to vertical edges of sacrificial regions 3441′ and 3441″are formed as illustrated further below. The dimension D_(OPEN-1) in theX direction is approximately 3F, where F is a minimum photolithographicdimension. For a 65 nm technology node, D_(OPEN-1) is 195 nm, which is anon-minimum and therefore non-critical dimension at any technology node.At this point in the process, sidewall spacer techniques are used toposition vertical sidewalls at a distance R from the inner surfaces ofsacrificial regions 3441′ and 3441″ as described further below.

Next, methods deposit a conformal sacrificial layer 3443 as illustratedin FIG. 34E. In some embodiments, the thickness of conformal sacrificiallayer 3443 is selected as R, which in this example is selected asapproximately F/2. In this example, since R is approximately F/2, andsince F is approximately 65 nm, then the thickness of conformalsacrificial layer 3443 is approximately 32.5 nm. Conformal sacrificiallayer 3443 may be formed using conductor, semiconductor, or insulatormaterials similar to those materials used to form sacrificial layer 3441described further above.

Next, methods directionally etch conformal sacrificial layer 3443 usingreactive ion etch (RIE) for example, using known industry methods,forming opening 3444 of dimension D_(OPEN-2) and sacrificial regions3443′ and 3443″, both having vertical sidewalls self-aligned andseparated from inner vertical sidewall of sacrificial regions 3441′ and3441″, respectively, by a distance R in the X direction as illustratedin FIG. 34F. Distance R is approximately equal to F/2, or approximately32.5 nm in this example. Dimension D_(OPEN-2) of opening 3444 isapproximately 2F, or approximately 130 nm for a 65 nm technology node, anon-critical dimension.

Next, methods directionally etch an opening through contact layer 3440to the top surface of insulator layer 3435. Directional etching usingRIE, for example, forms an opening of size D_(OPEN-2) of approximately2F (130 nm in this example) in contact layer 3440, and forms sidewallcontact regions 3440′ and 3440″ as illustrated in FIG. 34G.

Next, methods directionally etch an opening through insulator layer 3435to the top surface of contact layer 3430. Directional etching using RIE,for example, forms an opening 3444′ of size D_(OPEN-2) of approximately2F (130 nm in this example) in insulator layer 3435, and forms insulatorregions 3435′ and 3435″ as illustrated in FIG. 34H.

Next, methods deposit conformal nanotube element 3445 with vertical (Z)orientation on the sidewalls of opening 3444′ as illustrated in FIG.34I. The size of opening 3444′ is approximately the same as the size ofopening 3444. Conformal nanotube element 3445 may be 0.5 to 20 nm thick,for example, and may be fabricated as a single layer or as multiplelayers using deposition methods such as spin-on and spray-on methods.Nanotube element methods of fabrication are described in greater detailin the incorporated patent references.

Since nanotube element 3445 is in contact with contact layer 3430 andthe sidewalls of sidewall contact regions 3440′ and 3440″, separated bythe thickness of insulator region 3435′ and 3435″, respectively, twononvolatile nanotube switch channel regions are partially formed(channel width is not yet defined) having channel length L_(SW-CH) inthe Z direction corresponding to the thickness of insulator regions3435′ and 3435″ in the range of 5 nm to 250 nm as illustrated in FIG.34I. The vertical (Z-axis) portion of nanotube element 3445 is separatedfrom the inner vertical sidewalls of sacrificial regions 3441′ and 3441″by a self-aligned distance R. These partially formed verticalnonvolatile nanotube switches are similar to vertically orientednonvolatile nanotube elements 765 and 765′ of memory storage regions760A and 760B, respectively, illustrated in FIG. 7B. Conformal nanotubeelement 3445 is also in contact with sacrificial regions 3443′ and 3443″and sacrificial regions 3441′ and 3441″ as illustrated in FIG. 34I.

Next methods deposit conformal insulator layer 3450 on nanotube element3445 as an insulating and protective layer and reduces opening 3444′ toopening 3451 as illustrated in FIG. 34J. Opening 3451 is similar toopening 3444′, except for the addition of conformal insulator 3450 andconformal nanotube element 3445. Conformal insulator 3450 may be 5 to200 nm thick, for example, and may be formed from any known insulatormaterial in the CMOS industry, or packaging industry, for example suchas SiO₂, SiN, Al₂O₃, BeO, polyimide, PSG (phosphosilicate glass),photoresist, PVDF (polyvinylidene fluoride), sputtered glass, epoxyglass, and other dielectric materials and combinations of dielectricmaterials such as PVDF capped with an Al₂O₃ layer, for example.Insulator 3450 is deposited to a thickness sufficient to ensureprotection of nanotube element 3445 from high density plasma (HDP)deposition.

At this point in the process, it is desirable to partially fill opening3451 by increasing the thickness of the bottom portion of insulator 3450in the vertical (Z direction) on horizontal surfaces with little or nothickness increase on the sidewalls (vertical surfaces) of insulator3450, forming insulator 3450′. Exemplary industry methods of using HDPdeposition to fill openings with a dielectric layer are disclosed inU.S. Pat. No. 4,916,087, the entire contents of which are incorporatedherein by reference, for example. However, U.S. Pat. No. 4,916,087 fillsopenings by depositing dielectric material on horizontal and verticalsurfaces. Other methods of directional HDP insulator deposition may beused instead, e.g., by directionally depositing a dielectric materialsuch that more than 90% of the insulator material is deposited onhorizontal surfaces and less than 10% of the insulator material isdeposited on vertical surfaces with good thickness control. A shortisotropic etch may be used to remove insulator material deposited onvertical surfaces. The thickness of the additional dielectric materialis not critical. The additional dielectric material may be the same asthat of conformal insulator 3450 or may be a different dielectricmaterial. Dielectric material selection with respect to nanotubeelements is described in greater detail in U.S. patent application Ser.No. 11/280,786.

Next, methods directionally deposit an insulator material in opening3451 using known industry methods such as selective HDP insulatordeposition and increase insulator thickness primarily on horizontalsurfaces as illustrated by insulator 3450′ in opening 3451′ and on topsurfaces in FIG. 34K.

Next, methods deposit and planarize an insulator 3452 such as TEOSfilling opening 3451′ as illustrated in FIG. 34L.

Next, methods planarize the structure illustrated in FIG. 34L in orderto remove the top portion of insulator 3450′ and the top portion ofunderlying nanotube element 3445 as illustrated in FIG. 34M. The top ofsacrificial regions 3441′, 3441″, 3443′, and 3443″ may be used as CMPetch stop reference layers. Insulator 3450″ is the same as insulator3450′ except that the top horizontal layer has been removed. Nanotubeelement 3445′ is the same as nanotube element 3445 except that the tophorizontal layer has been removed. Insulator 3452′ is the same asinsulator 3452 except that insulator thickness has been reduced.

Next, methods etch (remove) sacrificial regions 3443′ and 3443″ andinsulator 3452′. Exposed vertical sidewalls of nanotube element 3445′and conformal insulator 3450″ remain as illustrated in FIG. 34N.

Next, methods etch (remove) the exposed portion of nanotube element3445′ forming nanotube element 3445″ as illustrated in FIG. 34O. Methodsof etching nanotube fabrics and elements are described in greater detailin the incorporated patent references.

Then, methods such as isotropic etch remove exposed portions ofinsulator 3450′ to form insulator 3450′″.

At this point in the process, sidewall spacer methods are applied asillustrated further below to form self aligned sacrificial regions to bereplaced further along in the fabrication process as illustrated furtherbelow by a conductor material to form the upper portion of nanotubeelement contacts and also to define self aligned trench regions to beused to define self-aligned cell dimensions along the X direction asalso illustrated further below. Using sidewall spacer methods to formself aligned structures without requiring masking and alignment resultsin minimum cell areas.

In this example, with respect to FIGS. 34P and 34Q, a self alignedsacrificial region of X dimension F is formed using methods similar tothose used in FIGS. 34E and 34F. Next, methods deposit a conformalsacrificial layer 3455 as illustrated in FIG. 34P. The thickness ofconformal sacrificial layer 3455 is selected as F. In this example,since F is approximately 65 nm, then the thickness of conformalsacrificial layer 3455 is approximately 65 nm. Conformal sacrificiallayer 3455 may be formed using conductor, semiconductor, or insulatormaterials similar to those materials used to form sacrificial layers3441 and 3443 described further above.

Next, methods directionally etch conformal sacrificial layer 3455 usingreactive ion etch (RIE) for example, using known industry methods,forming opening 3451″ of dimension approximately F, which in thisexample is approximately 65 nm as illustrated in FIG. 34Q. The innersidewalls of opening 3451″ are defined by sacrificial regions 3455′ and3455″ and are self-aligned to the inner walls of sacrificial regions3441′ and 3441″ and separated by a distance of approximately F. Theseinner walls will be used as illustrated further below to form one sideof an upper portion of a nanotube contact region and define one side ofa cell in the X direction.

Next, methods deposit and planarize a sacrificial layer to formsacrificial region 3456 coplanar with sacrificial regions 3455′, 3455″,3441′, and 3441″ as illustrated in FIG. 34R.

Next, methods apply CMP etching to reduce the thickness of sacrificialregion 3456 to form sacrificial region 3458; the thickness ofsacrificial regions 3455′ and 3455″ to form sacrificial regions 3455-1and 3455-2, respectively; and the thickness of sacrificial regions 3441′and 3441″ to form sacrificial regions 3458′ and 3458″, respectively asillustrated in FIG. 34S. Coplanar sacrificial regions 3458, 3458′,3458″, 3455-1, and 3455-2 have thickness values in the range of 10 nm200 nm, for example.

At this point in the process, sacrificial regions 3455-1 and 3455-2 maybe used as masking layers for directional etching of trenches usingmethods that define outer cell dimensions along the X direction for 3Dcells using one NV NT diode with cathode-to-nanotube connection. U.S.Pat. No. 5,670,803 to co-inventor Bertin discloses a 3-D array (in thisexample, 3D-SRAM) structure with simultaneously trench-defined sidewalldimensions. This structure includes vertical sidewalls simultaneouslydefined by trenches cutting through multiple layers of doped silicon andinsulated regions in order avoid multiple alignment steps. Such trenchdirectional selective etch methods may cut through multiple conductor,semiconductor, and oxide layers and stop on the top surface of asupporting insulator (SiO₂) layer between the 3D array structure and anunderlying semiconductor substrate. Trench 3459 is formed first and thenfilled with an insulator and planarized. Then, trenches 3459′, and 3459″are formed simultaneously and then filled and planarized as illustratedfurther below. Other corresponding trenches (not shown) are also etchedwhen forming the memory array structure. Exemplary method steps that maybe used to form trench regions 3459, 3459′, and 3459″ and then fill thetrenches to form insulating trench regions are described further below.

Sacrificial regions 3458′ and 3458″ that define the location of trenchregions 3459′ and 3459″ that are formed as described further below maybe blocked with a sacrificial noncritical masking layer (not shown),while methods form trench 3469 using known directional selective etchmethods such as reactive ion etch (RIE). Trench 3459 forms a first oftwo opposite vertical sidewalls in the X direction defining one side ofNV NT diode cells. Alternatively, sacrificial region 3458 that definesthe location of trench region 3459 that is formed further below may beetched selective to sacrificial regions 3458′ and 3458″ withoutrequiring a noncritical masking layer.

First, methods directionally selectively etch (remove) exposed regions(portions) of sacrificial region 3458 using known industry methods asillustrated in FIG. 34T.

Next, methods selectively etch exposed regions (portions) of conformalinsulator 3450′″ using known industry methods and form conformalinsulators 3450-1 and 3450-2 as illustrated in FIG. 34U.

Next, methods selectively etch exposed regions of nanotube element 3445″and form nanotube elements 3445-1 and 3445-2 as illustrated in FIG. 34U.Nanotube element methods of etching are described in greater detail inthe incorporated patent references.

Next, methods selectively etch exposed regions of contact layer 3430using known industry methods.

Next, methods selectively etch exposed regions of N+ polysilicon layer3425 using known industry methods.

Next, methods selectively etch exposed regions of N polysilicon layer3420 using known industry methods.

Next, methods selectively etch exposed regions of contact layer 3415using known industry methods.

Then, methods etch exposed regions of conductor layer 3410 using knownindustry methods, forming trench 3459. Directional etching stops at thesurface of planar insulator 3403.

Next, methods fill and planarize trench 3459 with an insulator such asTEOS for example forming insulator 3460 using known industry methods asillustrated in FIG. 34V.

Next, methods form a noncritical mask region (not shown) over insulator3460.

Next, sacrificial regions 3458′ and 3458″ are selectively etched(removed) as illustrated in FIG. 34W. With sacrificial regions 3458′ and3458″ removed and with insulator 3460 protected by a mask layer (notshown), methods form trenches 3469′ and 3469″ using known directionalselective etch techniques such as RIE. Trenches 3459′ and 3459″ form asecond vertical (Z) sidewall in the X direction of NV NT diode cells.

First, methods directionally selectively etch (remove) exposed portionsof contact 3440′ and 3440″ using known industry methods and expose aportion of the top surface of semiconductor layers 3435′ and 3435″ anddefine contact 3440-1 and 3440-2 regions as illustrated in FIG. 34X.

Next, methods selectively etch exposed portions of insulator regions3435′ and 3435″ using known industry methods and form insulator regions3435-1 and 3435-2.

Next, methods selectively etch exposed portions of contact regions 3430′and 3430″ using known industry methods and form contact regions 3430-1and 3430-2.

Next, methods selectively etch exposed portions of N+ polysilicon layer3425′ and 3425″ using known industry methods and form N+ polysiliconregions 3425-1 and 3425-2.

Next, methods selectively etch exposed portions of N polysilicon layer3420′ and 3420″ using known industry methods and form N polysiliconregions 3420-1 and 3420-2 as illustrated in FIG. 34X.

Next, methods selectively etch exposed regions of contact layer 3415′and 3415″ using known industry methods and form contact regions 3415-1and 3415-2.

Then, methods selectively etch exposed portions of conductor layer 3410′and 3410″ using known industry methods and form bit lines 3410-1 (BL0)and 3410-2 (BL1). Directional etching stops at the surface of planarinsulator 3403 as illustrated in FIG. 34X.

Next, methods deposit and planarize an insulator such as TEOS and filltrench openings 3459′ and 3459″ with insulators 3460′ and 3460″,respectively, as illustrated in FIG. 34Y.

Next, methods etch (remove) sacrificial regions 3455-1 and 3455-2.

Next, methods deposit and planarize conductor 3465′ to form upper layercontacts 3465-1 and 3465-2 as illustrated in FIGS. 34Z and 34AA.

Next, methods deposit and planarize conductive layer 3471 using knownindustry methods to form cross section 3470 as illustrated in FIG. 34BB.Cross section 3470 corresponds to cross section 2800 illustrated in FIG.28A. The methods described further above form a cross section (notshown) corresponding to cross section 2800′ illustrated in FIG. 28B ifprocess fabrication begins with FIG. 34A′ instead of FIG. 34A.

At this point in the process, cross section 3470 illustrated in FIG.34BB has been fabricated, and includes NV NT diode cell dimensions of 1F(where F is a minimum feature size) defined in the X direction as wellas corresponding array bit lines. Next, cell dimensions used to definedimensions in the Y direction are formed by directional trench etchprocesses similar to those described further above with respect to crosssection 3470 illustrated in FIG. 34BB. Trenches used to definedimensions in the Y direction are approximately orthogonal to trenchesused to define dimensions in the X direction. In this example, cellcharacteristics in the Y direction do not require self alignmenttechniques described further above with respect to X directiondimensions. Cross sections of structures in the Y direction areillustrated with respect to cross section A-A′ illustrated in FIG. 34BB.

Next, methods deposit and pattern a masking layer such as masking layer3473 on the surface of word line layer 3471 as illustrated in FIG. 34CC.Masking layer 3473 may be non-critically aligned to alignment marks inplanar insulator 3403. Openings 3474, 3474′, and 3474″ in mask layer3473 determine the location of trench directional etch regions, in thiscase trenches are approximately orthogonal to bit lines such as bit line3410-1 (BL0).

Next, methods form trenches 3475, 3475′, and 3475″ corresponding toopenings 3474, 3474′, and 3474″, respectively, in masking layer 3473.Trenches 3475, 3475′, and 3475″ form two sides of vertical sidewalls inthe Y direction defining two opposing sides of NV NT diode cells asillustrated in FIG. 34DD.

Then, methods directionally selectively etch (remove) exposed portionsof word line layer 3471 illustrated in FIG. 34DD using known industrymethods to form word lines 3471-1 (WL0) and 3471-2 (WL1) illustrated inFIG. 34DD.

Next, methods selectively etch exposed portions of contact region 3465-1illustrated in FIG. 34CC using known industry methods to form contacts3465-1′ and 3465-1″ as illustrated in FIG. 34DD.

Next, methods selectively etch exposed portions of contact region3440-1, nanotube element 3455-1, and conformal insulator 3450-1illustrated in FIG. 34BB using known industry methods to form contacts3440-1′ and 3440-1″, conformal insulator regions (not shown in FIG. 34DDcross section A-A′), and nanotube elements 3445-1′ and 3445-1″ asillustrated in FIG. 34DD.

Next, methods selectively etch exposed regions of insulators 3435-1,nanotube element 3455-1, and conformal insulator 3450-1 illustrated inFIG. 34BB using known industry methods to form insulator regions andconformal insulator regions (not shown in FIG. 34DD cross section A-A′)and nanotube elements 3445-1′ and 3445-1″ illustrated in FIG. 34DD.

Next, methods selectively etch exposed portions of contact regions3430-1 and 3430-2 illustrated in FIGS. 34BB and 34CC using knownindustry methods and form contacts 3430-1′ and 3430-1″ illustrated inFIG. 34DD (cross section A-A′).

Next, methods selectively etch exposed portions of N+ polysiliconregions 3425-1 and 3425-2 illustrated in FIG. 34BB using known industrymethods and form N+ polysilicon regions 3425-1′ and 3425-1″ illustratedin FIG. 34DD (cross section A-A′).

Next, methods selectively etch exposed portions of N polysilicon regions3420-1 and 3420-2 illustrated in FIG. 34BB using known industry methodsand form N polysilicon regions 3420-1′ and 3420-1″ illustrated in FIG.34DD (cross section A-A′).

Then, methods selectively etch exposed portions of contact regions3415-1 and 3415-2 illustrated in FIG. 34BB using known industry methodsand form insulators 3415-1′ and 3415-1″ illustrated in FIG. 34DD (crosssection A-A′). Directional etching stops at the surface of bit line3410-1.

Next, methods deposit insulator 3476 using known industry methods asillustrated in FIG. 34EE. Insulator 3476 may be TEOS, for example.

Then, methods planarize insulator 3476 to form insulator 3476′ usingknown industry methods and form cross section 3470′ illustrated in FIG.34FF. Cross section 3470′ illustrated in FIG. 34FF and cross section3470 illustrated in FIG. 34BB are two cross sectional representations ofthe same passivated NV NT diode vertically oriented cell. Cross section3470 illustrated in FIG. 34BB corresponds to cross section 2800illustrated in FIG. 28A.

At this point in the process, cross sections 3470 and 3470′ illustratedin FIGS. 34BB and 34FF, respectively, have been fabricated, nonvolatilenanotube element vertically-oriented channel length L_(SW-CH) andhorizontally-oriented channel width W_(SW-CH) are defined, includingoverall NV NT diode cell dimensions of 1F in the X direction and 1F inthe Y direction, as well as corresponding bit and word array lines.Cross section 3470 is a cross section of two adjacent verticallyoriented cathode-to-nanotube type nonvolatile nanotube diode-based cellsin the X direction and cross section 3470′ is a cross section of twoadjacent vertically oriented cathode-to-nanotube type nonvolatilenanotube diode-based cells in the cells in the Y direction. Crosssections 3470 and 3470′ include corresponding word line and bit linearray lines. The nonvolatile nanotube diodes form the steering andstorage elements in each cell illustrated in cross sections 3470 and3470′ each occupy a 1F by 1F area. The spacing between adjacent cells is1F so the cell periodicity can be as low as 2F in both the X and Ydirections. Therefore one bit can occupy an area of as low as 4F². Atthe 65 nm technology node, for example, the cell area is less than 0.02um².

Methods of Fabricating 3-Dimensional Cell Structure of Nonvolatile CellsUsing NV NT Devices Having Vertically Oriented Diodes and HorizontallyOriented NT Switches with Cathode-to-NT Switch Connection

Methods 2710 illustrated in FIG. 27A can be used to define supportcircuits and interconnects similar to those described with respect tomemory 2600 illustrated in FIG. 26A as described further above.Exemplary methods 2710 apply known semiconductor industry design andfabrication techniques to fabricated support circuits andinterconnections 3501 in and on a semiconductor substrate as illustratedin FIG. 35A. Support circuits and interconnections 3501 can include, forexample, FET devices in a semiconductor substrate and interconnectionssuch as vias and wiring above a semiconductor substrate.

Next, methods 2730 illustrated in FIG. 27B deposit and planarizeinsulator 3503 on the surface of support circuits and interconnections3501 layer.

Next, methods form interconnect contact 3507 through planar insulator3503 as illustrated in FIG. 35A. Contact 3507 through planar insulator3503 is in contact with support circuits and interconnections 3501. Thecombination of support circuits and interconnections 3501 and planarizedinsulator 3503 is referred to as memory support structure 3505 asillustrated in FIG. 35A.

Next, methods deposit a conductor layer 3510 on the planarized surfaceof insulator 3503 as illustrated in FIG. 35A, typically 50 to 500 nmthick, using known industry methods. Contact 3507 through planarinsulator 3503 connects conductor layer 3510 with support circuits andinterconnections 3501. Examples of conductor layer 3510 and contact 3507materials are elemental metals such as, Al, Au, W, Cu, Mo, Pd, Ni, Ru,Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu,TiPd, PbIn, and TiW, other suitable conductors, or conductive nitrides,oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).Materials such as those used in conductor layer 3410 may be used to formarray lines and also to form anodes for Schottky diodes.

Next, methods deposit an N polysilicon layer 3520 of thickness 10 nm to500 nm on the surface of conductor 3510. N polysilicon layer 3520 may bedoped with arsenic or phosphorus in the range of 10¹⁴ to 10¹⁷ dopantatoms/cm³, for example. N polysilicon layer 3520 may be used to formcathodes of Schottky diodes. In addition to doping levels, thepolysilicon crystalline size (or grain structure) of N Polysilicon layer3420 may also be controlled by known industry methods of deposition.Also, known industry SOI methods of deposition may be used that resultin polysilicon regions that are single crystalline (no longerpolysilicon), or nearly single crystalline.

Next, methods deposit N+ polysilicon layer 3525 on the surface of Npolysilicon layer 3520 as illustrated in FIG. 35A in order to form anohmic contact layer. N+ polysilicon layer 3525 is typically doped witharsenic or phosphorous to 10²⁰ dopant atoms/cm³, for example, and has athickness of 20 to 400 nm, for example.

Next, methods deposit an insulator layer 3530 on N+ layer 3525 asillustrated in FIG. 35B. The thickness of insulator layer 3530 may varyin thickness from 10 nm to greater than 400 nm, for example. Insulator3530 may be formed from any known insulator material in the CMOSindustry, or packaging industry, for example such as SiO₂, SiN, Al₂O₃,BeO, polyimide, PSG (phosphosilicate glass), photoresist, PVDF(polyvinylidene fluoride), sputtered glass, epoxy glass, and otherdielectric materials and combinations of dielectric materials such asPVDF capped with an Al₂O₃ layer, for example. U.S. patent applicationSer. No. 11/280,786 gives some examples of various dielectric materials.

At this point in the fabrication process, methods deposit contact layer3535 on the surface of insulator layer 3530 as illustrated in FIG. 35B.Contact layer 3535 may be 10 to 500 nm in thickness, for example.Contact layer 3535 may be formed using Al, Au, W, Cu, Mo, Pd, Ni, Ru,Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu,TiPd, PbIn, and TiW, other suitable conductors, or conductive nitrides,oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x),for example.

Next, methods directionally etch opening 3537 through contact layer 3535and insulator layer 3530 to the top surface of N+ polysilicon layer 3525as illustrated in FIG. 35C. Directional etching may use RIE, for example

Next methods deposit conformal insulator layer 3540′ in contact withsurface regions of contact 3535 and N+ polysilicon layer 3525 and onexposed sidewall surface regions of contact 3535 and insulator 3530 asillustrated in FIG. 35D. Conformal insulator 3540′ may be 5 to 250 nmthick, for example, and may be formed from any known insulator materialin the CMOS industry, or packaging industry, for example such as SiO₂,SiN, Al₂O₃, BeO, polyimide, PSG (phosphosilicate glass), photoresist,PVDF (polyvinylidene fluoride), sputtered glass, epoxy glass, and otherdielectric materials and combinations of dielectric materials such asPVDF capped with an Al₂O₃ layer, for example. Insulator 3540′ isdeposited to a thickness that forms nanotube element channel lengthregions as described further below with respect to 35I and insulates acontact described further below with respect to FIG. 35G from contactwith contact 3535.

Next, methods directionally etch insulator 3540′ using known industrymethods such as RIE and form sidewall spacer regions 3540 illustrated inFIG. 35E that define nanotube element channel length as describedfurther below with respect to FIG. 35I.

Next, methods deposit and planarize conductor 3545′ to form contact 3545as illustrated in FIGS. 35F and 35G.

Next, methods deposit conformal nanotube element 3550 on a coplanarsurface formed by contact 3535, sidewalls 3540, and contact 3545 asillustrated in FIG. 35H. Conformal nanotube element 3550 may be 0.5 to20 nm thick, for example, and may be fabricated as a single layer or asmultiple layers using deposition methods such as spin-on and spray-onmethods. Nanotube element methods of fabrication are described in theincorporated patent references.

Next, methods deposit insulator layer 3555 on nanotube element 3550 asan insulating and protective layer as illustrated in FIG. 35I. Thechannel length L_(SW-CH) of nanotube element 3550 is defined by thesurface dimension of sidewall spacers 3540. Insulator layer 3555 may be5 to 200 nm thick, for example, and may be formed from any appropriateknown insulator material in the CMOS industry, or packaging industry,for example such as SiO₂, SiN, Al₂O₃, BeO, polyimide, PSG(phosphosilicate glass), photoresist, PVDF (polyvinylidene fluoride),sputtered glass, epoxy glass, and other dielectric materials andcombinations of dielectric materials such as PVDF capped with an Al₂O₃layer, for example. Dielectric material selection with respect tonanotube elements is described in U.S. patent application Ser. No.11/280,786.

Next, methods pattern and etch opening 3560 as illustrated in FIG. 35Jto the top of contact 3535. Methods etch a portion of opening 3560 usingknown industry methods. Methods then etch the exposed region of nanotubeelement 3550 using ashing, for example, or other means described in theincorporated patent references.

Next, methods deposit and planarize conductor 3565′ to form contact 3565as illustrated in FIGS. 35K and 35L.

Next, masking layer 3570 is patterned in the X direction as illustratedin FIG. 35L and defines the openings for directional selective trenchetching to form trench regions 3572 and 3572′ described further belowwith respect to FIG. 35M.

Next, methods selectively etch exposed portions of insulator 3555 usingknown industry methods and form insulator region 3555′.

Next, methods selectively etch exposed regions of nanotube element 3550and form nanotube element 3550′ as illustrated in FIG. 35M. Nanotubeelement methods of etching are described in greater detail in theincorporated patent references.

Next, methods selectively etch exposed portions of contact 3535 usingknow industry methods and form contact region 3535′.

Next, methods selectively etch exposed portions of insulator 3530 andform insulator region 3530′.

Next, methods selectively etch exposed portions of N+ polysilicon layer3525 using known industry methods and form N+ polysilicon region 3525′.

Next, methods selectively etch exposed portions of N polysilicon layer3520 using known industry methods and form N polysilicon region 3520′ asillustrated in FIG. 35M.

Then, methods selectively etch exposed portions of conductor layer 3510using known industry methods and forms bit line 3510′ (BL0). Directionaletching stops at the surface of planar insulator 3503 as illustrated inFIG. 35M.

Next, methods deposit an insulator 3574 such as TEOS, for example, tofill trench openings 3572 and 3572′ and then methods planarize insulator3574 to form insulator 3574′ as illustrated in FIGS. 35N and 35O.

Next, methods deposit and planarize conductive layer 3575 correspondingto array word line WL0 using known industry methods to form crosssection 3580 as illustrated in FIG. 35P. Cross section 3580 correspondsto cross section 2800″ illustrated in FIG. 28C. Word line WL0orientation is along the X direction, and bit line BL0 orientation isalong the Y axis as shown further below.

At this point in the process, cross section 3580 illustrated in FIG. 35Phas been fabricated, and includes NV NT diode cell dimensions of 2-3F(where F is a minimum feature size) defined in the X direction as wellas corresponding array bit lines. Next, cell dimensions used to definedimensions in the Y direction are formed by directional trench etchprocesses similar to those described further above with respect to crosssection 3580 illustrated in FIG. 35P. Trenches used to define dimensionsin the Y direction are approximately orthogonal to trenches used todefine dimensions in the X direction. Cross sections of structures inthe Y direction are illustrated with respect to cross section X-X′illustrated in FIG. 35P.

Next, methods deposit and pattern a masking layer such as masking layer3581 on the surface of word line layer 3575′ as illustrated in FIG. 35Q.Masking layer 3581 may be non-critically aligned to alignment marks inplanar insulator 3503. Openings in mask layer 3581 determine thelocation of trench directional etch regions, in this case trenches areapproximately orthogonal to bit lines such as bit line 3510′ (BL0).

Next, methods form trenches 3582 and 3582′ corresponding to openings inmasking layer 3581. Trenches 3582 and 3582′ form two sides of verticalsidewalls in the Y direction defining two opposing sides of NV NT diodecells as illustrated in FIG. 35Q.

Next, methods directionally selectively etch (remove) exposed portionsof word line layer 3575 illustrated in FIG. 35P using known industrymethods to form word line 3575′ (WL0) illustrated in FIG. 35Q (crosssection X-X′).

Next, methods selectively etch exposed portions of insulator 3555′ asillustrated in FIG. 35Q (cross section X-X′) and also selectively etchexposed portions of contact 3565 (not shown in FIG. 35Q) using knownindustry methods to form insulator region 3555″ as illustrated in FIG.35Q and also to form a modified contact 3565 not shown in FIG. 35Q(cross section X-X′),

Next, methods selectively etch (remove) exposed portions of nanotubeelement 3550′ forming nanotube element 3550″ as illustrated in FIG. 35Q.Nanotube element methods of etching are described in greater detail inthe incorporated patent references.

Next, methods selectively etch exposed portions of contact 3545 formingcontact 3545′ as illustrated in FIG. 35Q (cross section X-X′); methodsalso selectively etch exposed portions of sidewall spacers 3540 to formmodified sidewall spacers 3440 not illustrated in FIG. 35Q; and methodsalso selectively etch exposed portions of contact 3535 to form modifiedcontacts 3535 not illustrated in FIG. 35Q.

Next, methods selectively etch exposed portions of insulator 3530′ toform a modified insulator 3530′ not illustrated in FIG. 35Q (crosssection X-X′).

Next, methods selectively etch exposed portions of N+ polysiliconregions 3525′ illustrated using known industry methods and form N+polysilicon region 3525″ illustrated in FIG. 35Q (cross section X-X′).

Next, methods selectively etch exposed portions of N polysilicon regions3520′ illustrated using known industry methods and form N+ polysiliconregion 3520″ illustrated in FIG. 35Q (cross section X-X′). Directionalselective etch stops at the surface of bit line 3510′ (BL0).

Next, methods deposit insulator 3585 using known industry methods asillustrated in FIG. 35R. Insulator 3585 may be TEOS, for example.

Then, methods planarize insulator 3585 to form insulator 3585′ usingknown industry methods and form cross section 3580′ illustrated in FIG.35S. Cross section 3580′ illustrated in FIG. 35S and cross section 3580illustrated in FIG. 35P are two cross sectional representations of thesame embodiment of a passivated NV NT diode with a vertically orienteddiode and a horizontally nonvolatile nanotube switch. Cross section 3480illustrated in FIG. 35P corresponds to cross section 2800″ illustratedin FIG. 28C.

Methods of Fabricating Nonvolatile Memories Using NV NT Diode Deviceswith Anode-to-NT Switch Connection

Exemplary methods 3000 illustrated in FIGS. 30A and 30B may be used tofabricate embodiments of memories using NV NT diode devices withanode-to-NT switch connections for vertically oriented NV NT switchessuch as those shown in cross section 3100 illustrated in FIG. 31A, crosssection 3100′ illustrated in FIG. 31B, and cross section 3100″illustrated in FIG. 31C as described further below with respect to FIG.36. Structures such as cross section 3000, 3000′, and 3000″ may be usedto fabricate memory 2900 illustrated schematically in FIG. 29A.

Exemplary methods of fabricating cross sections 3000, 3000′, and 3000″can be performed using critical alignments in Y direction process steps.There are no critical alignments in the X direction because in thisexample distance between trenches determines the width of the nanotubeelement. However, the width of the nanotube element may be formed to beless than the trench-to-trench spacing by using methods similar to thosedescribed further below with respect to the Y direction. In the Ydirection, critical alignment requirements can be eliminated by usingmethods that form self-aligned internal cell vertical sidewalls thatdefine vertical nanotube channel element location, vertical channelelement length (L_(SW) _(—) _(CH)), and form nanotube channel elementcontacts with respect to trench sidewalls that are etched later in theprocess to define outer cell dimensions using methods of fabricationdescribed further below with respect to FIG. 36. In this example, NV NTdiode cell structures occupy a minimum dimension F in the X and Ydirections, where F is a minimum photolithographic dimension. In thisexample, the internal cell vertical sidewall is positioned (by selfalignment techniques) at approximately R distance from trench sidewallsthat are separated by distance F and that define outer cell dimensionsas illustrated further below with respect to FIGS. 36A-36FF. FIGS.36A-36FF are illustrated with a spacing R of approximately F/2. However,methods using self alignment techniques, such as those described furtherbelow with respect to FIG. 36A-36FF, may position a vertical sidewall atany location R within the cell region of width F using R values of F/4,F/3, F/2, 3F/4, etc for example. In some embodiments, R is not relatedin any particular way to F.

Methods of Fabricating 3-Dimensional Cell Structure of Nonvolatile CellsUsing NV NT Devices Having Vertically Oriented Diodes and VerticallyOriented NT Switches with Anode-to-NT Switch Connection

Exemplary methods 3010 illustrated in FIG. 30A can be used to definesupport circuits and interconnects similar to those described withrespect to memory 2900 illustrated in FIG. 29A as described furtherabove. Methods 3010 apply known semiconductor industry techniques designand fabrication techniques to fabricated support circuits andinterconnections 3601 in and on a semiconductor substrate as illustratedin FIG. 36A. Support circuits and interconnections 3601 include FETdevices in a semiconductor substrate and interconnections such as viasand wiring above a semiconductor substrate.

Next, methods 3030 illustrated in FIG. 30B deposit and planarizeinsulator 3603 on the surface of support circuits and interconnections3601 layer. Interconnect means through planar insulator 3603, not shownin FIG. 36A, are shown further above with respect to FIGS. 35A-35S. Thecombination of support circuits and interconnections 3601 and planarizedinsulator 3603 is referred to as memory support structure 3605 asillustrated in FIG. 34A.

Next, methods deposit a conductor layer 3610 on the planarized surfaceof insulator 3603 as illustrated in FIG. 36A, typically 50 to 500 nmthick, using known industry methods. Examples of conductors layermaterials are elemental metals such as, Al, Au, W, Cu, Mo, Pd, Ni, Ru,Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu,TiPd, PbIn, and TiW, other suitable conductors, or conductive nitrides,oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).

Next, methods deposit N+ polysilicon layer 3620 on the surface ofconductor layer 3610 as illustrated in FIG. 36A in order to form anohmic contact layer. N+ polysilicon layer 3620 is typically doped witharsenic or phosphorous to 10²⁰ dopant atoms/cm³, for example, and has athickness of 20 to 400 nm, for example.

Next, methods deposit an N polysilicon layer 3625 of thickness 10 nm to500 nm on the surface of N+ polysilicon layer 3620. N polysilicon layer3625 may be doped with arsenic or phosphorus in the range of 10¹⁴ to10¹⁷ dopant atoms/cm³, for example. N polysilicon layer 3625 may be usedto form cathodes of Schottky diodes. In addition to doping levels, thepolysilicon crystalline size (or grain structure) of N polysilicon layer3625 may also be controlled by known industry methods of deposition.Also, known industry SOI methods of deposition may be used that resultin polysilicon regions that are single crystalline (no longerpolysilicon), or nearly single crystalline.

Next, methods deposit contact layer 3630 on the surface of N polysiliconlayer 3625 forming a Schottky diode anode layer. Contact layer 3630 mayalso be used to form lower level contacts for nanotube elements asillustrated further below with respect to FIG. 36I. Contact layer 3630may have a thickness range of 10 to 500 nm, for example. Contact layer3630 may use similar materials to those used in forming conductor layer3610; or contact layer 3630 material may be chosen to optimize anodematerial for enhanced Schottky diode properties such lower forwardvoltage drop and/or lower diode leakage. Anode contact layer 3630 mayinclude Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo, Na, Ni, Os, Pb, Pd,Pt, Rb, Ru, Ti, W, Zn and other elemental metals. Also, silicides suchas CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂, and ZrSi₂ may be used;or contact layer 3630 may be formed in layers to include conductivematerial for forming optimized Schottky diode characteristics on a lowerlayer and conductive materials to optimize ohmic contact to nanotubeelements on an upper layer.

At this point in the process, remaining methods may be used to fabricateNV NT diode using Schottky diode-based anode-to-NT switch structuressuch as those illustrated in FIG. 31A. However, as described furtherabove with respect to FIG. 31B for example, NV NT diodes may be formedusing PN diodes instead of Schottky diodes. Therefore, alternatively, aPN diode alternative fabrication method is illustrated in FIG. 34A′.

Methods 3000 described further above, and with respect to FIG. 36A, mayalso be used to describe the fabrication of FIG. 36A′. Support circuitsand interconnections 3601′ illustrated in FIG. 36A′ correspond tosupport circuits and interconnections 3601 illustrated in FIG. 36A,except for possible small changes that may be introduced in individualcircuits to accommodate differences in diode characteristics such asturn-on voltage, for example, between Schottky diodes and PN diodes.

Next, methods deposit planarized insulator 3603′ on the surface ofsupport circuits and interconnections 3601′ as illustrated in FIG. 36A′.Planarized insulator 3603′ corresponds to planarized insulator 3603except for possible small changes that may be introduced in insulator3603′ to accommodate differences in diode characteristics. Memorysupport structure 3605′ is therefore similar to support structures 3605except for small changes that may be introduced in support circuits andinterconnections 3601′ and planarized insulator 3603′ as describedfurther above with respect to FIG. 36A′.

Next, methods deposit conductor layer 3610′ in contact with the surfaceof planarized insulator 3603′ as illustrated in FIG. 36A′ which can besimilar in thickness and materials to conductor layer 3610 describedfurther above with respect to FIG. 36A.

Next, methods deposit N+ polysilicon layer 3620′ on the surface ofconductor layer 3610′ as illustrated in FIG. 36A′ in order to form anohmic contact layer. N+ polysilicon layer 3620′ is typically doped witharsenic or phosphorous to 10²⁰ dopant atoms/cm³, for example, and has athickness of 20 to 400 nm, for example.

Next, methods deposit an N polysilicon layer 3625′ of thickness 10 nm to500 nm on the surface of N+ polysilicon layer 3620′. N polysilicon layer3625′ may be doped with arsenic or phosphorus in the range of 10¹⁴ to10¹⁷ dopant atoms/cm³, for example. N polysilicon layer 3625′ may beused to form cathodes of Schottky diodes. In addition to doping levels,the polysilicon crystalline size (or grain structure) of N polysiliconlayer 3625′ may also be controlled by known industry methods ofdeposition. Also, known industry SOI methods of deposition may be usedthat result in polysilicon regions that are single crystalline (nolonger polysilicon), or nearly single crystalline.

Next, methods deposit a P polysilicon layer 3627 of thickness 10 nm to500 nm on the surface of N polysilicon layer 3625′ as illustrated inFIG. 36A′. P polysilicon layer 3627 may be doped with boron in the rangeof 10¹⁴ to 10¹⁷ dopant atoms/cm³, for example. P polysilicon layer 3627may be used to form anodes of PN diodes. In addition to doping levels,the polysilicon crystalline size of P Polysilicon layer 3627 may also becontrolled by known industry methods of deposition. Also, known industrySOI methods of deposition may be used that result in polysilicon regionsthat are single crystalline (no longer polysilicon), or nearly singlecrystalline.

Next, methods deposit contact layer 3630′ on the surface of Ppolysilicon layer 3627 forming an ohmic contact between contact layer3630′ and P polysilicon layer 3627. Contact layer 3630′ may also be usedto form lower level contacts for nanotube elements as illustratedfurther below with respect to FIG. 36I.

At this point in the process, remaining methods may be used to fabricateNV NT diode using PN diode-based anode-to-NT switch structures such asthose illustrated in FIG. 31B. However, as described further above withrespect to FIG. 31C for example, NV NT diodes may be formed using bothSchottky diodes and PN diodes in parallel. Therefore, alternatively, acombined parallel Schottky diode and PN diode alternative fabricationmethod is illustrated in FIG. 34A″.

Methods 3000 described further above, and with respect to FIG. 36A, mayalso be used to describe the fabrication of FIG. 36A″. Support circuitsand interconnections 3601″ illustrated in FIG. 36A″ correspond tosupport circuits and interconnections 3601 illustrated in FIG. 36A,except for possible small changes that may be introduced in individualcircuits to accommodate differences in diode characteristics such asturn-on voltage, for example, between Schottky diodes and combinedparallel Schottky diode and PN diodes.

Next, methods deposit conductor layer 3610″ in contact with the surfaceof planarized insulator 3603″ as illustrated in FIG. 36A″ which issimilar in thickness and materials to conductor layer 3610 describedfurther above with respect to FIG. 36A.

Next, methods deposit N+ polysilicon layer 3620″ on the surface ofconductor layer 3610″ as illustrated in FIG. 36A″ in order to form anohmic contact layer. N+ polysilicon layer 3620″ is typically doped witharsenic or phosphorous to 10²⁰ dopant atoms/cm³, for example, and has athickness of 20 to 400 nm, for example.

Next, methods deposit an N polysilicon layer 3625″ of thickness 10 nm to500 nm on the surface of N+ polysilicon layer 3620″. N polysilicon layer3625″ may be doped with arsenic or phosphorus in the range of 10¹⁴ to10¹⁷ dopant atoms/cm³, for example. N polysilicon layer 3625″ may beused to form cathodes of both Schottky diodes and PN diodes in parallel.In addition to doping levels, the polysilicon crystalline size (or grainstructure) of N polysilicon layer 3625″ may also be controlled by knownindustry methods of deposition. Also, known industry SOI methods ofdeposition may be used that result in polysilicon regions that aresingle crystalline (no longer polysilicon), or nearly singlecrystalline.

At this point in the process, remaining methods may be used to fabricateNV NT diodes using Schottky diodes and PN diode in parallel to formanode-to-NT switch structures such as those illustrated in FIG. 31C.Schottky diodes and PN diodes in parallel may be formed as illustratedfurther below with respect to FIG. 36I if contact layer 3630 is omittedfrom the structure.

Schottky diodes and PN diodes in parallel are formed because a nanotubeelement such as nanotube element 3645 illustrated further below withrespect to FIG. 36I, if contact layer 3630 is omitted from thestructure, would be in contact with N poly layer 3625. P-typesemiconductor nanotube elements, a subset of NT elements 3645, would bein physical and electrical contact with N polysilicon layer 3625, andwould form PN diode-anodes and N polysilicon layer 3625 form cathodesthat together form PN diodes. Metallic type nanotube elements, also asubset of NT elements 3645, would also be in physical and electricalcontact with N polysilicon layer 3625, and would form Schottkydiode-anodes and N polysilicon layer 3625 would form cathodes forSchottky diodes having Schottky diode junctions as part of combined PNand Schottky diode junctions in parallel.

Descriptions of methods of fabrication continue with respect toSchottky-diode based structures described with respect to FIG. 36A toform NV NT diode cell structures corresponding to cross section 3100illustrated in FIG. 31A. However, these methods of fabrication may alsobe applied to the PN diode-based structures described with respect toFIG. 36A′ to form NV NT diode cell structures corresponding to crosssection 3100′ illustrated in FIG. 31B. Also, these methods offabrication may also be applied to structures with respect to FIG. 36A″to form NV NT diode cell structure corresponding to cross section 3100″illustrated in FIG. 31C.

At this point in process, fabrication continues by using methods todeposit an insulator layer 3635 on contact layer 3630 as illustrated inFIG. 36B. The thickness of insulator layer 3635 may be well controlledand used to determine the channel length of vertically orientednonvolatile nanotube switches as illustrated further below with respectto FIG. 36I. The thickness of insulator layer 3635 may vary in thicknessfrom less than 5 nm to greater than 250 nm, for example. Insulator 3635may be formed from any appropriate known insulator material in the CMOSindustry, or packaging industry, for example such as SiO₂, SiN, Al₂O₃,BeO, polyimide, PSG (phosphosilicate glass), photoresist, PVDF(polyvinylidene fluoride), sputtered glass, epoxy glass, and otherdielectric materials and combinations of dielectric materials such asPVDF capped with an Al₂O₃ layer, for example. U.S. patent applicationSer. No. 11/280,786 includes some examples of various dielectricmaterials.

Next, methods deposit contact layer 3640 on insulator layer 3635 asillustrated in FIG. 36B. Contact layer 3640 may be in the range of 10 to500 nm thick, for example, and may be formed using various conductormaterials similar to materials described with respect to contact 3630described further above.

Next methods deposit sacrificial layer 3641 on contact layer 3640 asillustrated in FIG. 36C. Sacrificial layer 3641 may be in the range of10 to 500 nm thick and be formed using conductor, semiconductor, orinsulator materials such as materials described further above withrespect to contact layer 3630, semiconductor layers 3620 and 3625, andinsulator layer 3635.

Next, methods deposit and pattern a masking layer such as masking layer3642 deposited on the top surface of sacrificial layer 3641 asillustrated in FIG. 36C using known industry methods. The mask openingmay be aligned to alignment marks in planar insulating layer 3603 forexample; the alignment is not critical.

Then, methods directionally etch sacrificial layer 3641 to form anopening of dimension D_(OPEN-1′) in the Y direction through sacrificiallayer 3641 stopping at the surface of contact layer 3640 using knownindustry methods as illustrated in FIG. 36D. Two memory cells thatinclude vertical nanotube channel elements self aligned and positionedwith respect to vertical edges of sacrificial regions 3641′ and 3641″are formed as illustrated further below. The dimension D_(OPEN-1′) inthe Y direction is approximately 3F, where F is a minimumphotolithographic dimension. For a 65 nm technology node, D_(OPEN-1′) is195 nm, which is a non-minimum and therefore non-critical dimension atany technology node. At this point in the process, sidewall spacertechniques are used to position vertical sidewalls at a distance R fromthe inner surfaces of sacrificial regions 3641′ and 3641″ as describedfurther below.

Next, methods deposit a conformal sacrificial layer 3643 as illustratedin FIG. 36E. The thickness of conformal sacrificial layer 3643 can beselected as R, which in this example is selected as approximately F/2.In this example, since R is approximately F/2, and since F isapproximately 65 nm, then the thickness of conformal sacrificial layer3643 is approximately 32.5 nm. Conformal sacrificial layer 3643 may beformed using conductor, semiconductor, or insulator materials similar tothose materials used to form sacrificial layer 3641 described furtherabove.

Next, methods directionally etch conformal sacrificial layer 3643 usingreactive ion etch (RIE) for example, using known industry methods,forming opening 3644 of dimension D_(OPEN-2′) and sacrificial regions3643′ and 3643″, both having vertical sidewalls self-aligned andseparated from inner vertical sidewall of sacrificial regions 3641′ and3641″, respectively, by a distance R in the Y direction as illustratedin FIG. 36F. Distance R is approximately equal to F/2, or approximately32.5 nm in this example. Dimension D_(OPEN-2′) of opening 3644 isapproximately 2F, or approximately 130 nm for a 65 nm technology node, anon-critical dimension.

Next, methods directionally etch an opening through contact layer 3640to the top surface of insulator layer 3635. Directional etching usingRIE, for example, forms an opening of size D_(OPEN-2′) of approximately2F (130 nm in this example) in contact layer 3640, and forms sidewallcontact regions 3640′ and 3640″ as illustrated in FIG. 36G.

Next, methods directionally etch an opening through insulator layer 3635to the top surface of contact layer 3630. Directional etching using RIE,for example, forms an opening 3644′ of size D_(OPEN-2′) of approximately2F (130 nm in this example) in insulator layer 3635, and forms insulatorregions 3635′ and 3635″ as illustrated in FIG. 36H.

Next, methods deposit conformal nanotube element 3645 with vertical (Z)orientation on the sidewalls of opening 3644′ as illustrated in FIG.36I. The size of opening 3644′ is approximately the same as the size ofopening 3644. Conformal nanotube element 3645 may be 0.5 to 20 nm thick,for example, and may be fabricated as a single layer or as multiplelayers using deposition methods such as spin-on and spray-on methods.Nanotube element methods of fabrication are described in greater detailin the incorporated patent references.

Since nanotube element 3645 is in contact with contact layer 3630 andthe sidewalls of sidewall contact regions 3640′ and 3640″, separated bythe thickness of insulator region 3635′ and 3635″, respectively, twononvolatile nanotube switch channel regions are partially formed(channel width is not yet defined) having channel length L_(SW-CH) inthe Z direction corresponding to the thickness of insulator regions3635′ and 3635″ in the range of 5 nm to 250 nm as illustrated in FIG.36I. The vertical (Z-axis) portion of nanotube element 3645 is separatedfrom the inner vertical sidewalls of sacrificial regions 3641′ and 3641″by a self-aligned distance R. These partially formed verticalnonvolatile nanotube switches are similar to vertically orientednonvolatile nanotube elements 765 and 765′ of memory storage regions760A and 760B, respectively, illustrated in FIG. 7B. Conformal nanotubeelement 3645 is also in contact with sacrificial regions 3643′ and 3643″and sacrificial regions 3641′ and 3641″ as illustrated in FIG. 36I.

Next methods deposit conformal insulator layer 3650 on nanotube element3645 as an insulating and protective layer and reduces opening 3644′ toopening 3651 as illustrated in FIG. 36J. Opening 3651 is similar toopening 3644′, except for the addition of conformal insulator 3650 andconformal nanotube element 3645. Conformal insulator 3650 may be 5 to200 nm thick, for example, and may be formed from any known insulatormaterial in the CMOS industry, or packaging industry, for example suchas SiO₂, SiN, Al₂O₃, BeO, polyimide, PSG (phosphosilicate glass),photoresist, PVDF (polyvinylidene fluoride), sputtered glass, epoxyglass, and other dielectric materials and combinations of dielectricmaterials such as PVDF capped with an Al₂O₃ layer, for example.Insulator 3650 is deposited to a thickness sufficient to ensureprotection of nanotube element 3645 from high density plasma (HDP)deposition.

At this point in the process, it is desirable to partially fill opening3651 by increasing the thickness of the bottom portion of insulator 3650in the vertical (Z direction) on horizontal surfaces with little or nothickness increase on the sidewalls (vertical surfaces) of insulator3650 as described above. The thickness of the additional dielectricmaterial is not critical. The additional dielectric material may be thesame as that of conformal insulator 3650 or may be a differentdielectric material. Dielectric material selection with respect tonanotube elements is described in greater detail in U.S. patentapplication Ser. No. 11/280,786.

Next, methods directionally deposit an insulator material in opening3651 using known industry methods such as directional HDP insulatordeposition and increase insulator thickness primarily on horizontalsurfaces as illustrated by insulator 3650′ in opening 3651 and on topsurfaces in FIG. 36K, forming opening 3651′.

Next, methods deposit and planarize an insulator 3652 such as TEOSfilling opening 3651′ as illustrated in FIG. 36L.

Next, methods planarize the structure illustrated in FIG. 36L in orderto remove the top portion of insulator 3650′ and the top portion ofunderlying nanotube element 3645 as illustrated in FIG. 36M. The top ofsacrificial regions 3641′, 3641″, 3643′, and 3643″ may be used as CMPetch stop reference layers. Insulator 3650″ is the same as insulator3650′ except that the top horizontal layer has been removed. Nanotubeelement 3645′ is the same as nanotube element 3645 except that the tophorizontal layer has been removed. Insulator 3652′ is the same asinsulator 3652 except that insulator thickness has been reduced.

Next, methods etch (remove) sacrificial regions 3643′ and 3643″ andinsulator 3652′. Exposed vertical sidewalls of nanotube element 3645′and conformal insulator 3650″ remain as illustrated in FIG. 36N.

Next, methods etch (remove) the exposed portion of nanotube element3645′ forming nanotube element 3645″ as illustrated in FIG. 36O. Methodsof forming nanotube elements are described in greater detail in theincorporated patent references.

Then, methods such as isotropic etch remove exposed portions ofinsulator 3650′ to form insulator 3650′″ as illustrated in FIG. 36O.

At this point in the process, sidewall spacer methods are applied asillustrated further below to form self aligned sacrificial regions to bereplaced further along in the fabrication process as illustrated furtherbelow by a conductor material to form the upper portion of nanotubeelement contacts and also to define self aligned trench regions to beused to define self-aligned cell dimensions along the Y direction asalso illustrated further below. Using sidewall spacer methods to formself aligned structures without requiring masking and alignment canresult in cell areas of reduced size.

In this example, with respect to FIGS. 36P and 36Q, a self alignedsacrificial region of X dimension F is formed using methods similar tothose used in FIGS. 36E and 36F. Next, methods deposit a conformalsacrificial layer 3655 as illustrated in FIG. 36P. The thickness ofconformal sacrificial layer 3655 is selected as F. In this example,since F is approximately 65 nm, then the thickness of conformalsacrificial layer 3655 is approximately 65 nm. Conformal sacrificiallayer 3655 may be formed using conductor, semiconductor, or insulatormaterials similar to those materials used to form sacrificial layers3641 and 3643 described further above.

Next, methods directionally etch conformal sacrificial layer 3655 usingreactive ion etch (RIE) for example, using known industry methods,forming opening 3651″ of dimension approximately F, which in thisexample is approximately 65 nm as illustrated in FIG. 36Q. The innersidewalls of opening 3651″ are self-aligned to the inner walls ofsacrificial regions 3641′ and 3641″ and separated by a distance ofapproximately F. These inner walls will be used as illustrated furtherbelow to form one side of an upper portion of a nanotube contact regionand define one side of a cell in the Y direction.

Next, methods deposit and planarized a sacrificial layer to formsacrificial region 3656 coplanar with sacrificial regions 3655′, 3655″,3641′, and 3641″ as illustrated in FIG. 36R.

Next, methods apply CMP etching to reduce the thickness of sacrificialregion 3656 to form sacrificial region 3658; the thickness ofsacrificial regions 3655′ and 3655″ to form sacrificial regions 3655-1and 3655-2, respectively; and the thickness of sacrificial regions 3641′and 3641″ to form sacrificial regions 3658′ and 3658″, respectively asillustrated in FIG. 36S. Coplanar sacrificial regions 3658, 3658′,3658″, 3655-1, and 3655-2 have thickness values in the range of 10 nm200 nm, for example.

At this point in the process, sacrificial regions 3655-1 and 3655-2 maybe used as masking layers for directional etching of trenches usingmethods that define outer cell dimensions along the Y direction for 3Dcells using one NV NT diode with cathode-to-nanotube connection. Trench3659 is formed first and then filled with an insulator and planarized.Then, trenches 3659′, and 3659″ are formed simultaneously and thenfilled and planarized as illustrated further below. Other correspondingtrenches (not shown) are also etched when forming the memory arraystructure. Exemplary method steps that may be used to form trenchregions 3659, 3659′, and 3659″ and then fill the trenches to forminsulating trench regions are described further below.

Sacrificial regions 3658′ and 3658″ that define the location of trenchregions 3659′ and 3659″ that are formed as described further below maybe blocked with a sacrificial noncritical masking layer (not shown),while methods form trench 3659 using known directional selective etchmethods such as reactive ion etch (RIE). Trench 3659 forms a first oftwo opposite vertical sidewalls in the Y direction defining one side ofNV NT diode cells. Alternatively, sacrificial region 3658 that definesthe location of trench region 3659 that is formed further below may beetched selective to sacrificial regions 3658′ and 3658″ withoutrequiring a noncritical masking layer.

First, methods directionally selectively etch (remove) exposed regions(portions) of sacrificial region 3658 using known industry methods asillustrated in FIG. 36T.

Next, methods selectively etch exposed regions (portions) of conformalinsulator 3650′″ using known industry methods and form conformalinsulators 3650-1 and 3650-2 as illustrated in FIG. 36U.

Next, methods selectively etch exposed regions of nanotube element 3645″and form nanotube elements 3645-1 and 3645-2 as illustrated in FIG. 36U.Nanotube element methods of etching are described in greater detail inthe incorporated patent references.

Next, methods selectively etch exposed regions of contact layer 3630using known industry methods forming contact layer regions 3630′ and3630″.

Next, methods selectively etch exposed regions of N polysilicon layer3625 forming regions 3625′ and 3625″ using known industry methods.

Next, methods selectively etch exposed regions of N+ polysilicon layer3620 forming regions 3620′ and 3620″ using known industry methods.

Then, methods etch exposed regions of conductor layer 3610 using knownindustry methods forming conductor regions 3610′ and 3610″. Directionaletching stops at the surface of planar insulator 3603.

Next, methods fill and planarize trench 3659 with an insulator such asTEOS for example and forming insulator 3660 using known industry methodsas illustrated in FIG. 36V.

Next, methods form a noncritical mask region (not shown) over insulator3660.

Next, sacrificial regions 3658′ and 3658″ are selectively etched asillustrated in FIG. 36W. With sacrificial regions 3658′ and 3658″removed and with insulator 3660 protected by a mask layer (not shown),methods form trenches 3659′ and 3659″ using known directional selectiveetch techniques such as RIE as shown in FIG. 36 X. Trenches 3659′ and3659″ form a second vertical (Z) sidewall in the Y direction of NV NTdiode cells.

To form trenches 3659′ and 3659″, methods directionally selectively etch(remove) exposed portions of contact 3640′ and 3640″ using knownindustry methods and expose a portion of the top surface of insulatorlayers 3635′ and 3635″ and define contact 3640-1 and 3640-2 regions asillustrated in FIG. 36X.

Next, methods selectively etch exposed portions of insulator regions3635′ and 3635″ using known industry methods and form insulator regions3635-1 and 3635-2.

Next, methods selectively etch exposed portions of contact regions 3630′and 3630″ using know industry methods and form contact regions 3630-1and 3630-2.

Next, methods selectively etch exposed portions of N polysilicon layer3625′ and 3625″ using known industry methods and form N polysiliconregions 3625-1 and 3625-2.

Next, methods selectively etch exposed portions of N+ polysilicon layer3620′ and 3620″ using known industry methods and form N+ polysiliconregions 3620-1 and 3620-2 as illustrated in FIG. 36X.

Then, methods selectively etch exposed portions of conductor layer 3410′and 3410″ using known industry methods and form word lines 3610-1 (WL0)and 3610-2 (WL1). Directional etching stops at the surface of planarinsulator 3603 as illustrated in FIG. 36X.

Next, methods deposit and planarize an insulator such as TEOS and filltrench openings 3659′ and 3659″ with insulators 3660′ and 3660″,respectively, as illustrated in FIG. 36Y.

Next, methods etch (remove) sacrificial regions 3655-1 and 3655-2.

Next, methods deposit and planarize conductor 3665′ to form upper layercontacts 3665-1 and 3665-2 as illustrated in FIGS. 36Z and 36AA.

Next, methods deposit and planarize conductive layer 3671 using knownindustry methods to form cross section 3670 as illustrated in FIG. 36BB.Cross section 3670 corresponds to cross section 3100 illustrated in FIG.31A. In some embodiments, methods described further above form a crosssection (not shown) corresponding to cross section 3100′ illustrated inFIG. 31B if process fabrication begins with FIG. 34A′ instead of FIG.34A. Also, in some embodiments, methods described further above form across section (not shown) corresponding to cross section 3100″illustrated in FIG. 31C if process fabrication begins with FIG. 34A″.

At this point in the process, cross section 3670 illustrated in FIG.36BB has been fabricated, and includes NV NT diode cell dimensions of 1F(where F is a minimum feature size) defined in the Y direction as wellas corresponding array bit lines. Next, cell dimensions used to definedimensions in the X direction are formed by directional trench etchprocesses similar to those described further above with respect to crosssection 3670 illustrated in FIG. 36BB. Trenches used to definedimensions in the X direction are approximately orthogonal to trenchesused to define dimensions in the Y direction. In this example, cellcharacteristics in the X direction do not require self alignmenttechniques described further above with respect to Y directiondimensions. Cross sections of structures in the X direction areillustrated with respect to cross section B-B′ illustrated in FIG. 36BB.

Next, methods deposit and pattern a masking layer such as masking layer3673 on the surface of bit line conductor layer 3671 as illustrated inFIG. 36CC. Masking layer 3673 may be non-critically aligned to alignmentmarks in planar insulator 3603. Openings 3674, 3674′, and 3674″ in masklayer 3673 determine the location of trench directional etch regions, inthis case trenches are approximately orthogonal to bit lines such asword line 3410-1 (WL0).

Next, methods form trenches 3675, 3675′, and 3675″ corresponding toopenings 3674, 3674′, and 3674″, respectively, in masking layer 3673.Trenches 3675, 3675′, and 3675″ form two sides of vertical sidewalls inthe X direction defining two opposing sides of NV NT diode cells asillustrated in FIG. 36DD.

Methods directionally selectively etch (remove) exposed portions of bitline conductive layer 3671 illustrated in FIG. 36DD using known industrymethods to form bit lines 3671-1 (BL0) and 3671-2 (BL1) illustrated inFIG. 36DD.

Next, methods selectively etch exposed portions of contact regions3665-1 and 3665-2 illustrated in FIG. 36CC using known industry methodsto form contacts 3665-1′ and 3665-1″ as illustrated in FIG. 36DD.

Next, methods selectively etch exposed portions of contact regions3640-1 and 3640-2, nanotube elements 3645-1 and 3645-2, and conformalinsulators 3650-1 and 3650-2 illustrated in FIG. 36BB using knownindustry methods to form contacts 3640-1′ and 3640-1″, conformalinsulator regions (not shown in FIG. 36DD cross section B-B′), andnanotube elements 3645-1′ and 3645-1″ as illustrated in FIG. 36DD.

Next, methods selectively etch exposed regions of insulators 3635-1 and3635-2 using known industry methods to form insulator regions 3635-1′and 3635-1″ illustrated in FIG. 36DD.

Next, methods selectively etch exposed portions of contact regions3630-1 and 3630-2 illustrated in FIGS. 36BB and 36CC using knownindustry methods and form contacts 3630-1′ and 3630-1″ illustrated inFIG. 36DD (cross section B-B′)

Next, methods selectively etch exposed portions of N polysilicon regions3625-1 and 3625-2 illustrated in FIG. 36BB using known industry methodsand form N polysilicon regions 3625-1′ and 3625-1″ illustrated in FIG.36DD (cross section B-B′).

Next, methods selectively etch exposed portions of N+ polysiliconregions 3620-1 and 3620-2 illustrated in FIG. 36BB using known industrymethods and form N+ polysilicon regions 3620-1′ and 3620-1″ illustratedin FIG. 36DD (cross section B-B′). Directional etching stops at thesurface of word line 3610-1 (WL0).

Next, methods deposit insulator 3676 using known industry methods asillustrated in FIG. 36EE. Insulator 3676 may be TEOS, for example.

Then, methods planarize insulator 3676 to form insulator 3676′ usingknown industry methods and form cross section 3670′ illustrated in FIG.36FF. Cross section 3670′ illustrated in FIG. 36FF and cross section3670 illustrated in FIG. 36BB are two cross sectional representation ofthe same embodiment of a passivated NV NT diode vertically orientedcell. Cross section 3670 illustrated in FIG. 36BB corresponds to crosssection 3100 illustrated in FIG. 31A.

At this point in the process, cross sections 3670 and 3670′ illustratedin FIGS. 36BB and 36FF, respectively, have been fabricated, nonvolatilenanotube element vertically-oriented channel length L_(SW-CH) andhorizontally-oriented channel width W_(SW-CH) are defined, includingoverall NV NT diode cell dimensions of 1F in the Y direction and 1F inthe X direction, as well as corresponding bit and word array lines.Cross section 3670 is a cross section of two adjacent verticallyoriented anode-to-nanotube type nonvolatile nanotube diode-based cellsin the Y direction and cross section 3670′ is a cross section of twoadjacent vertically oriented anode-to-nanotube type nonvolatile nanotubediode-based cells in the cells in the X direction. Cross sections 3670and 3670′ include corresponding word line and bit line array lines. Thenonvolatile nanotube diodes form the steering and storage elements ineach cell illustrated in cross sections 3670 and 3670′ and each occupy a1F by 1F area. The spacing between adjacent cells is 1F so the cellperiodicity is 2F in both the X and Y directions. Therefore one bitoccupies an area of 4F². At the 65 nm technology node, the cell area isless than 0.02 um².

Methods of Fabricating Nonvolatile Memories Using NV NT Diode DeviceStacks with Both Anode-to-NT Switch Connections and Cathode-to-NT SwitchConnections

Some embodiments of methods of fabricating stacked memory arrays areshown in methods 3200 illustrated in FIG. 32 and described furtherabove. First, methods 3210 fabricate support circuits andinterconnections on semiconductor substrate, then insulate and planarizeas described further above with respect to FIGS. 34 and 36.

Next, cathode-on-nanotube methods of fabrication to form lower array3310 illustrated FIG. 33B and corresponding lower array 3310′illustrated in FIG. 33B′ are described further above with respect toFIG. 34.

Next, anode-on-nanotube methods of fabrication to form upper array 3320illustrated in FIG. 33B and corresponding upper array 3320′ with sharedword line 3330 and corresponding word line 3330′ are described furtherabove with respect to FIG. 36. The only difference is that methodsillustrated in FIG. 36 are applied on the planarized top surface oflower array 3310 and 3310′ with shared word line wiring shared betweenboth lower and upper arrays.

Nonvolatile 3D Memories Using Vertically-Oriented Nonvolatile NanotubeSwitches Having Nanotube Elements of Varying Configurations for EnhancedPerformance and Density

Vertically-oriented cathode-to-NT and anode-to-NT nonvolatile nanotubediode-based 3D structures described further above illustrate a thinnanotube element, where these thin nanotube elements are typically lessthan 10 nm thick (1-5 nm, for example), and thin relative to horizontaldimensions of the nonvolatile nanotube diode cell boundaries.Cathode-to-nanotube nonvolatile nanotube diode examples are illustratedin cross section 2800 in FIG. 28A and cross section 3470 illustrated inFIG. 34BB. Anode-to-nanotube nonvolatile nanotube diode examples areillustrated in cross section 3100 illustrated in FIG. 31A and crosssection 3670 illustrated in FIG. 36BB. Nonvolatile nanotube switchesthat form the data storage portion of nonvolatile nanotube diodes arethe same for cathode-on-NT and anode-on-NT diodes. Therefore, cellstructures described further below illustrating various nonvolatilenanotube switch configurations show the select (steering) diode portionof nonvolatile nanotube device structures in schematic form.

FIGS. 6A-6B and 7A-7B illustrate horizontally and vertically-orientednanotube (nanofabric) layers, respectively, composed of networks ofnanotubes forming nanotube (nanofabric) layers and nanotube elementswhen patterned. As cell dimensions are reduced, from approximately 150to 20 nm for example, the number of nanotubes in contact with nanotubeterminals (contacts) is reduced for the same nanotube density (nanotubesper unit area). In order to compensate for reduced numbers ofnanotube-to-smaller terminal connections, the nanotube density(nanotubes per unit area) may be increased by optimizing individuallayer deposition and by depositing multiple nanotube layers usingspin-on and/or spray-on nanotube deposition techniques as described ingreater detail in the incorporated patent references. The result is thatnanotube (nanofabric) layers and patterned nanotube elements mayincrease in thickness as cell dimensions decrease. Nanotube (nanofabric)layer enhancement is described further below with respect to FIG. 38.

Structural (geometrical) details described further below illustratevarious options for nonvolatile nanotube switches. Nonvolatile nanotubeswitches of various thicknesses may be formed within isolationtrench-defined cell boundaries using nanotube elements of varyingthickness in order to optimized nonvolatile nanotube switch propertiesas illustrated further below with respect to FIGS. 37, 39, and 40.

Nonvolatile nanotube switches of various thicknesses may also be formedwithin isolation trench regions, outside isolation trench-defined cellboundaries, using nanotube elements of varying thickness as illustratedfurther below with respect to FIGS. 42A-42H and 43A-43B.

Nonvolatile nanotube switches of various thicknesses may also be formedboth within isolation trench-defined cell boundaries and withinisolation trench regions as illustrated further below with respect toFIG. 44A-44B.

Twice (2×) the storage density may be achieved without stacking arrays,as described further above with respect to FIG. 33, by storing two bitsper 3D cell using two nonvolatile nanotube switches that share oneselect (steering) diode as illustrated further below with respect toFIGS. 45 and 46.

Nonvolatile 3D Memories Using Vertically-Oriented Nonvolatile NanotubeSwitches Having Nanotube Elements of Varying Thicknesses

FIG. 37 illustrates cross section 3700 that includes two mirror imagecells, cell 1 and cell 2 and insulating trenches A, B, and C forming theboundaries of cells 1 and 2. Cells 1 and 2 are vertically-orientednonvolatile nanotube diodes. The select (steering) diode portion isrepresented schematically using schematic representation 3725 by diodesD1-1 and D1-2; the nonvolatile nanotube switch storage elements areillustrated in mirror image cross sections. Select (steering) diode D1-1combined with nonvolatile nanotube switch 3705 forms a cathode-on-NTnonvolatile nanotube diode cell; select (steering) diode D1-2 combinedwith nonvolatile nanotube switch 3705 forms an anode-on-NT nanotubediode cell. Nonvolatile nanotube switch 3705′ in cell 2 is a mirrorimage of nonvolatile nanotube switch 3705 in cell 1. Cross section 3700will be described primarily with respect to cell 1 and nonvolatilenanotube switch 3705.

Cross section 3700 illustrated in FIG. 37 is illustrated with relativelythin nanotube element 3745 in contact with a vertical sidewall locatedat a distance R of approximately F/2, where F is a minimum dimension forthe corresponding technology node. Cross section 3700 illustrated inFIG. 37 corresponds to cross section 2800 in FIG. 28 and cross section3470 illustrated in FIG. 34BB if select (steering) diode D1-1 is chosen,and cross section 3700 corresponds to cross section 3100 in FIG. 31A andcross section 3670 in FIG. 36BB if select (steering) diode D1-2 isselected. In both cases nonvolatile nanotube switch 3705 is the same.

For cell 1 formed using diode D1-1, array line 3710 illustrated in crosssection 3700 corresponds to array bit line 2810-1 shown in cross section2800 illustrated in FIG. 28A; diode D1-1 illustrated schematically inFIG. 37 corresponds to a Schtottky diode with junction 2818-1 andcorresponding structures in FIG. 28A. However, diode D1-1 may alsocorrespond to a PN diode with junction 2819-1 and correspondingstructures illustrated in FIG. 28B. Lower level contact 3730 illustratedin FIG. 37 corresponds to lower level contact 2830-1 illustrated in FIG.28A; insulator 3735 corresponds to insulator 2835-1 used to definenanotube element channel length L_(SW-CH); sidewall contact 3740corresponds to sidewall contact 2840-1; nanotube element 3745corresponds to nanotube element 2845-1; upper level contact 3765corresponds to upper level contact 2865-1; insulator 3750 corresponds toinsulator 2850-1; and array line 3771 corresponds to array word line2871.

For cell 1 formed using diode D1-2, array line 3710 illustrated in crosssection 3700 corresponds to array word line 3110-1 shown in crosssection 3100 illustrated in FIG. 31A; diode D1-2 illustratedschematically in FIG. 37 corresponds to a Schtottky diode with junction3133-1 and corresponding structures in FIG. 31A. However, diode D1-2 mayalso correspond to a PN diode with junction 3128-1 and correspondingstructures illustrated in FIG. 31B. Also, diode D1-2 may also correspondto combined Schottky and PN diode with junction 3147-1 and correspondingstructures illustrated in FIG. 31C. Lower level contact 3730 illustratedin FIG. 37 corresponds to lower level contact 3130-1 illustrated in FIG.31A; insulator 3735 corresponds to insulator 3135-1 used to definenanotube element channel length L_(SW-CH); sidewall contact 3740corresponds to sidewall contact 3140-1; nanotube element 3745corresponds to nanotube element 3145-1; upper level contact 3765corresponds to upper level contact 3165-1; insulator 3750 corresponds toinsulator 3150-1; and array line 3771 corresponds to array bit line3171.

Networks of nanotubes forming relatively thin nanotube (nanofabric)layers and corresponding nanotube elements typically have a nanotubedensity of approximately 500 nanotubes per square micrometer (um²).Nanotube layers and corresponding nanotube element typically includevoids, regions between nanotubes. Void areas may be relatively large,greater than 0.0192 um² for example, or may be relatively small, lessthan 0.0192 um² for example. As cell dimensions are reduced, nanotubedensity is increased with a corresponding decrease in void area and anincrease in nanotube layer and corresponding nanotube element thickness.FIGS. 6A-6B and 7A-7B illustrate relatively thin nanotube element 630and relatively thin nanotube layer 700, respectively, applied on asubstrate by spin-on methods at a nanotube density of up to 500nanotubes per um² with relatively large void areas. FIG. 38 illustratesnanotube layer 3800 formed on a substrate by spray-on methods withrelatively small void areas. For example, nanotube layer 3800 has novoids greater than 0.0192 um². Nanotube layer 3800 also has no voidareas between 0.0096 and 0.0192 um²; no void areas between 0.0048 and0.0096 um2; a relatively small number of void areas 3810 between 0.0024and 0048 um²; with most void areas such as void area 3820 less than0.0024 um².

For a technology node (generation) with F approximately 45 nm and ananotube element thickness of approximately 10 nm for example, thelocation R of a vertical sidewall may be at approximately F/2 orapproximately 22 nm as illustrated by nanotube element 3745 ofnonvolatile nanotube switch 3705 in cross section 3700 illustrated inFIG. 37. In this case, sidewall contact 3740 is approximately 22 nm andinsulator 3750 is approximately 13 nm. A region of upper level contact3765 to sidewall contact 3740 is approximately 22 nm. A region of lowerlevel contact 3730 to nanotube element 3745 is approximately 22 nm.

FIG. 39 illustrates cross section 3900 and includes nonvolatile nanotubeswitch 3905 in which the thickness of nanotube element 3745′ issubstantially greater than the thickness of nanotube element 3745illustrated in FIG. 37. Nonvolatile nanotube switch structures 3705 and3905 are fabricated using self aligned methods of fabrication asdescribed further above with respect to FIGS. 34 and 36. For atechnology node (generation) with F approximately 32 nm and a nanotubeelement thickness of approximately 15 nm for example, the location R ofa vertical sidewall may be at approximately F/3 or approximately 10 nmas illustrated by nanotube element 3745′ of nonvolatile nanotube switch3905 in cross section 3900 illustrated in FIG. 39. In this case,sidewall contact 3740′ is approximately 10 nm and insulator 3750′ isapproximately 7 nm. A region of upper level contact 3765′ to sidewallcontact 3740′ is approximately 10 nm. A region of lower level contactnanotube element 3745′ is approximately 22 nm.

FIG. 40 illustrates cross section 4000 and includes nanotube switch 4005in which the thickness of nanotube element 4050 is equal to the celldimension F. In this example, nanotube element 4050 may be deposited byspray-on methods of fabrication for example. For a technology node(generation) with F approximately 22 nm and a nanotube element thicknessof approximately 22 nm for example, the nanotube region fills theavailable cell region. A sidewall contact is eliminated and lower levelcontact 4030 and upper level contact 4065 form the two terminal(contact) regions to nanotube 4050.

Nonvolatile 3D Memories Using Vertically-Oriented Nonvolatile NanotubeSwitches Having Nanotube Elements within Trench Isolation Regions

FIGS. 37, 39, and 40 described further above show that as technologynodes (generations) reduce minimum dimensions F, and nanotubes elementsincrease thickness to reduce void areas, in some embodiments nanotubeelements may eventually fill the region available within the insulatingtrench-defined cell region and thus prevent further increase in nanotubeelement thickness. It is possible to continue to increase nanotubeelement overall thickness by also forming nanotube elements within theinsulating trench region as illustrated further below. Alternatively,nanotube elements may be placed wholly outside the insulating trenchregion and not within the cell boundaries as illustrated further below.

FIGS. 41A-41B are representations of a process for selectively formingvertical sidewall elements of controlled dimensions within and on avertical sidewall of a concave (trench) structure as described in U.S.Pat. No. 5,096,849, the entire contents of which are incorporated hereinby reference, to co-inventor Bertin. The process described in U.S. Pat.No. 5,096,849 includes filling a trench with resist material to beremoved, or alternatively, filling a trench with an insulator, forexample, that remains in the trench region. Next, RIE is used toprecisely remove the resist or insulator to a controlled depth d1 asmeasured from a top surface reference. Then, a conformal layer of amaterial of controlled thickness is deposited. Next, RIE is use toremove the conformal layer on horizontal surfaces leaving the conformallayer on the vertical sidewall of the trench. Next, a second resist orinsulator fills the remaining trench opening. Next, RIE is used toprecisely remove the sidewall film and resist or insulator to acontrolled depth of d2. At this point in the process vertical sidewallelements of vertical dimension d1-d2 and controlled thickness have beenformed. If the trench is filled with resist, the resist may be removed.If the trench is filled with an insulator material, the insulatormaterial may remain in the trench. Then, the trench is filled with aninsulator and planarized.

FIG. 41A illustrates a representation of a trench with outer walls 4110.A lower portion of the trench is filled with an insulator 4115, SiO₂ forexample, whose top surface is at a controlled depth d1 from the trenchsurface. A conformal layer is deposited and RIE removes conformal layermaterial on horizontal surfaces leaving partially completed verticalelements 4120 and 4120′. A resist or insulator 4130 fills the trenchregion above the top surface of resist or insulator 4115.

FIG. 41B illustrates a representation of FIG. 41A after using RIE toremove resist or insulator material 4130 and then vertical sidewallelements 4120 and 4120′ to a controlled depth d2 and forming filledregion 4130′ and vertical sidewall elements 4145 and 4145′. Verticalsidewall elements 4145 and 4145′ are of vertical dimensions d1-d2 andcontrolled known thickness defined by the thickness of the conformallayer material. Resist or insulator 4130′ may be removed or may be leftin place. Then, trench opening may be filled with insulating materialand planarized.

FIGS. 42A-42H illustrates methods of fabrication used to adapt theelements of U.S. Pat. No. 5,096,849 illustrated in FIG. 41 to formnanotube elements within isolation trenches described further above withrespect to FIGS. 28A-28C, 31A-31C, 33A-33D, 34A-34FF, 36A-36FF, 37, 39,and 40.

FIG. 42A illustrates an opening 4205 formed in an insulation trenchusing methods such as a selective controlled etch using RIE, forexample, with sidewall regions defining vertical surfaces of lower levelcontacts 4210 and 4210′, upper level contacts 4220 and 4220′, andinsulator 4215 and 4215′ between respective upper and lower levelcontacts, where the thickness of insulator 4215 and 4215′ define thechannel length L_(SW-CH) of nanotube elements as shown further below inFIG. 42D.

First, methods fill trench opening 4205 with an insulator 4225, TEOS forexample as illustrated in FIG. 42B.

Next, methods selectively etch insulator 4225 using a selective andcontrolled RIE etch to a depth D1 from a surface reference asillustrated in FIG. 42C.

Next, methods deposit conformal nanotube layer 4235 using methodsdescribed in greater detail in the incorporated patent references. Atthis point in the process, channel length L_(SW-CH) is defined asillustrated in FIG. 42D.

Then, methods deposit a protective conformal insulator layer 4240 asillustrated in FIG. 42D. Conformal insulator 4240 may be 5 to 50 nmthick, for example, and may be formed from any appropriate knowninsulator material in the CMOS industry, or packaging industry, forexample such as SiO₂, SiN, Al₂O₃, BeO, polyimide, PSG (phosphosilicateglass), photoresist, PVDF (polyvinylidene fluoride), sputtered glass,epoxy glass, and other dielectric materials and combinations ofdielectric materials such as PVDF capped with an Al₂O₃ layer, forexample, such as described in U.S. patent application Ser. No.11/280,786. Insulator 4240 is deposited to a thickness sufficient toensure protection of nanotube element 4235 from RIE etching.

Next, methods directly etch conformal insulator 4240 and nanotube layer4235 using RIE and remove conformal layer material on top horizontalsurfaces and bottom horizontal surfaces at the bottom of trench opening4241, leaving partially completed vertical elements 4240′, 4240″, 4235′,and 4235″ as illustrated in FIG. 42E.

Next methods fill trench opening 4241 with insulator 4242 such as TEOSfor example as illustrated in FIG. 42F.

Next, methods selectively etch insulator 4242, conformal insulators4240′ and 4240″, and nanotube elements 4235′ and 4235″ using a selectiveand controlled RIE etch to a depth D2 from a surface reference asillustrated in FIG. 42G. At this point in the process, insulator 4242′is formed; nanotube elements 4245 and 4245′ are formed; conformalinsulator 4250 and 4250′ are formed, and trench opening 4255 remains.

Then, methods fill trench opening 4255 with an insulator such as TEOSand methods planarize to form insulator 4260. At this point in theprocess cross section 4275 is formed, including nanotube channelelements 4270 and 4270′. Nanotube channel element 4270 includes nanotubeelement 4245 and conformal insulator 4250, and nanotube channel element4270′ includes nanotube element 4245′ and conformal insulator 4250′.Nanotube channel elements 4270 and 4270′ are in contact with a portionof vertical sidewalls of an upper level contact and a lower levelcontact, and are also in contact with an insulating layer that definesL_(SW-CH). For example, nanotube channel element 4270 is in contact withupper level contact 4220, lower level contact 4210, and insulator 4215,and nanotube channel element 4270′ is in contact with upper levelcontact 4220′, lower contact 4210′, and insulator 4215′.

Nantotube channel elements 4270 and 4270′ may be used instead ofnanotube element 3745 illustrated in FIG. 37 and nanotube element 3745′illustrated in FIG. 39 to form new nonvolatile nanotube switchstructures as illustrated in FIGS. 43A, 43B, and 43C. New cellstructures may be cathode-on-NT or anode-on-NT type cells. FIGS. 43A,43B, and 43C are shown for cathode-on-NT type cells for ease ofcomparison with FIG. 28A and FIGS. 34A-34FF described further above.

FIG. 43A illustrates cross section 4300 in which nonvolatile nanotubechannel element storage devices are positioned within isolating trench Bas illustrated by nonvolatile channel element 4370-1 positioned on thesidewall of a region of cell 1 and 4370-2 positioned on a region of cell2, which correspond to nonvolatile channel element 4270 and 4270′,respectively, illustrated by cross section 4275 in FIG. 42H. Crosssection 4300 illustrated in FIG. 43A shows relatively thin nanotubeelements 4345-1 and 4345-2 that may be, e.g., less than 10 nm thick.Nanotube element 4345-1 of nanotube channel element 4370-1 includessidewall contacts to lower level contact 4330-1 and upper level contact4365-1 of cell 1. Nonvolatile nanotube switch 4305-1 is formed by lowerlevel contact 4330-1 and upper level contact 4365-1, both in contactwith nanotube element 4345-1 of nanotube channel element 4370-1.Nanotube element 4345-2 of nanotube channel element 4370-2 includessidewall contacts to lower level contact 4330-2 and upper level contact4365-2 of cell 2. Nonvolatile nanotube switch 4305-2 is formed by lowerlevel contact 4330-2 and upper level contact 4365-2, both in contactwith nanotube element 4345-2 of nanotube channel element 4370-2. Cell 1and cell 2 are greater than minimum dimension F in the X direction,however, overall cell periodicity remains 2F and array density remainsunchanged.

FIG. 43B illustrates cross section 4300′ in which nonvolatile nanotubechannel element storage devices are positioned within isolating trenchB′ as illustrated by nonvolatile channel element 4370-1′ positioned onthe sidewall of a region of cell 1′ and 4370-2′ positioned on a regionof cell 2′, which correspond to nonvolatile channel element 4270 and4270′, respectively, illustrated by cross section 4275 in FIG. 42H.Cross section 4300′ illustrated in FIG. 43B shows relatively thicknanotube elements 4345-1′ and 4345-2′ that may be, e.g., 15 nm thick.Nanotube element 4345-1′ of nanotube channel element 4370-1′ includessidewall contacts to lower level contact 4330-1′ and upper level contact4365-1′ of cell 1′. Nonvolatile nanotube switch 4305-1′ is formed bylower level contact 4330-1′ and upper level contact 4365-1′, both incontact with nanotube element 4345-1′ of nanotube channel element4370-1′. Nanotube element 4345-2′ of nanotube channel element 4370-2′includes sidewall contacts to lower level contact 4330-2′ and upperlevel contact 4365-2′ of cell 2′. Nonvolatile nanotube switch 4305-2′ isformed by lower level contact 4330-2′ and upper level contact 4365-2′,both in contact with nanotube element 4345-2′ of nanotube channelelement 4370-2′. Cell 1′ and cell 2′ are greater than minimum dimensionF in the X direction, however, overall cell periodicity remains 2F andarray density remains unchanged.

FIG. 43C illustrates cross section 4300″ in which nonvolatile nanotubechannel element storage devices are positioned within isolating trenchA″, trench B″, and trench C″ as illustrated by nonvolatile channelelements 4370-1″ and 4370-3 positioned on sidewalls of regions of cell1″ and nonvolatile channel elements 4370-2″ and 4370-4 positioned onsidewalls of regions of cell 2″. Cross section 4300″ illustrated in FIG.43C shows relatively thick channel elements 4345-1″, 4345-2″, 4345-3,and 4345-4 that may be, e.g., 15 nm thick. Nanotube elements of nanotubechannel element 4370-1″ and 4370-3 include sidewall contacts to lowerlevel contact 4330-1″ and upper level contact 4365-1″ of cell 1″.Nonvolatile nanotube switch 4305-1″ is formed by lower level contact4330-1″ and upper level contact 4365-1″, both in contact with nanotubeelements 4345-1″ and 4345-3 of nanotube channel elements 4370-1″ and4370-3, respectively, for an effective channel element thickness of 30nm, for example. Nanotube elements of nanotube channel element 4370-2″and 4370-4 include sidewall contacts to lower level contact 4330-2″ andupper level contact 4365-2″ of cell 2″. Nonvolatile nanotube switch4305-2″ is formed by lower level contact 4330-2″ and upper level contact4365-2″, both in contact with nanotube elements 4345-2″ and 4345-4 ofnanotube channel elements 4370-2″ and 4370-4, respectively, for aneffective channel element thickness of 30 nm, for example. Cell 1″ andcell 2″ are greater than minimum dimension F in the X direction,however, overall cell periodicity remains 2F and array density remainsunchanged. As cells become much smaller, e.g., 22 nm and even less, thenthe number of nanotube elements between contacts decreases and theresistance goes up. There are limits to the nanotube density per layerthat can be achieved. Therefore, it can be useful to find ways to addlayers of nanotubes to try to keep the number of nanotubes nearly thesame (if possible) by putting more nanotube layers in parallel. In otherwords, the nanotube elements can be scaled to keep up with semiconductorscaling.

Nonvolatile 3D Memories Using Vertically-Oriented Nonvolatile NanotubeSwitches Having Nanotube Elements Stacked Above Steering (Select) Diodesand within Trench Isolation Regions

Nanotube elements included in nonvolatile nanotube switches may beincorporated within cell boundaries defined by isolation trenches asdescribed further above with respect to FIGS. 37 and 39, and also withrespect to structures illustrated in FIGS. 28A-28C and 31A-31C and withrespect to methods of fabrication described with respect to FIGS.34A-34FF and 36A-36FF. Also, nanotube elements included in nonvolatilenanotube switches may also be incorporated within isolation trenchregions and outside cell boundaries as described further above withrespect to FIGS. 43A-43C and methods of fabrication described withrespect to FIGS. 42A-42H. However, it is possible to combine nanotubeelements within cell boundaries and other nanotube elements in isolationtrenches outside cell boundaries to form nonvolatile nanotube switchesthat include both types of nanotube configurations. As cells become muchsmaller, e.g., 22 nm and even less, then the number of nanotube elementsbetween contacts decreases and the resistance goes up. There are limitsto the nanotube density per layer that can be achieved. Therefore, itcan be useful to find ways to add layers of nanotubes to try to keep thenumber of nanotubes nearly the same (if possible) by putting morenanotube layers in parallel. In other words, the nanotube elements canbe scaled to keep up with semiconductor scaling.

FIG. 44A illustrates cell 1 and mirror image cell 2 with nonvolatilenanotube switches 4405 and 4405′. Since cell 2 is a mirror image of cell1, only cell 1 will be described in detail. Nonvolatile nanotube switch4405 is formed by combining nonvolatile nanotube switch 4468corresponding to nonvolatile nanotube switch 3905 illustrated in FIG. 39and nanotube channel element 4470 corresponding to nanotube channelelement 4370-3 illustrated in FIG. 43C. Nonvolatile nanotube switch 4405may be formed by first forming nonvolatile nanotube switch 4468 usingmethods of fabrication described further above with respect to FIGS.34A-34FF. Next, nanotube channel element 4470 is formed using methods offabrication described with respect to FIGS. 42A-42H. Nanotube element4445 of nanotube channel element 4470 shares lower level contact 4430with nanotube element 4445′, and shares sidewall contact 4440 and upperlevel contact 4465 with nanotube element 4445′. Both nanotube element4445 and 4445′ have approximately the same channel length L_(SW-CH), inthe range of less than 5 nm to greater than 250 nm for example.Thickness values of nanotube element 4445 and 4445′ may be differentvalues. In this example, minimum dimension F is assumed to be 32 nm andthe thickness of each nanotube element may be 15 nm for an effectivethickness of 30 nm for combined nanotube elements 4445 and 4445′. Theeffective thickness 30 nm of combined nanotube elements 4445 and 4445′is approximately equal to the cell dimension F of 32 nm because nanotubeelements are used both inside the cell boundaries, and outside the cellboundaries, within isolation trench regions. While this exampleillustrates cathode-on-NT type cells, anode-on-NT cells may also beformed.

Nanotube elements included in nonvolatile nanotube switches may beincorporated within cell boundaries defined by isolation trenches asdescribed further above with respect to FIG. 40. Also, nanotube elementsincluded in nonvolatile nanotube switches may also be incorporatedwithin isolation trench regions and outside cell boundaries as describedfurther above with respect to FIGS. 43A-43C and methods of fabricationdescribed with respect to FIGS. 42A-42H. However, it is possible tocombine nanotube elements within cell boundaries and other nanotubeelements in isolation trenches outside cell boundaries to formnonvolatile nanotube switches that include both types of nanotubeconfigurations.

FIG. 44B illustrates cell 1 and cell 2 with nonvolatile nanotubeswitches 4405″ and 4405′″. Since cell 2 is of the same as cell 1, onlycell 1 will be described in detail. Nonvolatile nanotube switch 4405″ isformed by combining nonvolatile nanotube switch 4469 corresponding tononvolatile nanotube switch 4050 illustrated in FIG. 40 and nanotubechannel elements 4470-1 and 4470-2 corresponding to nanotube channelelement 4370-3 and 4370-1″, respectively, illustrated in FIG. 43C.Nonvolatile nanotube switch 4405″ may be formed by first formingnonvolatile nanotube switch 4469 using methods of fabrication similar tothose of FIG. 40. Next, nanotube channel elements 4470-1 and 4470-2 areformed using methods of fabrication described with respect to FIG. 42.Nanotube elements 4445-1 of nanotube channel element 4470-1 and nanotubeelement 4445-2 of nanotube channel element 4470-2 share lower levelcontact 4430 with nanotube element 4445-3, and share upper level contact4465 with nanotube element 4445-3. Nanotube elements 4445-1, 4445-2 and4445-3 have approximately the same channel length L_(SW-CH), in therange of less than 5 nm to greater than 150 nm for example. Thicknessvalues of nanotube elements 4445-1, 4445-2, and 4445-3 may be differentvalues. In this example, minimum dimension F is assumed to be 22 nm andthe thickness of nanotube elements 4445-1 and 4445-2 may be 6 nm eachand nanotube element 4445-3 may be 22 nm for a combined effectivethickness of 34 nm for combined nanotube elements 4445-1, 4445-2, and4445-3. The effective thickness 34 nm of combined nanotube elements4445-1, 4445-2, and 4445-3 is approximately 50% greater than celldimension F of 22 nm because nanotube elements are used both inside thecell boundaries, and outside the cell boundaries, within isolationtrench regions. While this example illustrates cathode-on-NT type cells,anode-on-NT cells may also be formed. As cells become much smaller,e.g., 22 nm and even less, then the number of nanotube elements betweencontacts decreases and the resistance goes up. There are limits to thenanotube density per layer that can be achieved. Therefore, it can beuseful to find ways to add layers of nanotubes to try to keep the numberof nanotubes nearly the same (if possible) by putting more nanotubelayers in parallel. In other words, the nanotube elements can be scaledto keep up with semiconductor scaling.

Nonvolatile 3D Memories Storing Two Bits Per Cell Using TwoVertically-Oriented Nonvolatile Nanotube Switches Sharing a SingleSteering (Select) Diode

FIGS. 33A-33D illustrate two stacked memory arrays, one cathode-on-NTtype array and the other an anode-on-NT type array to double bitdensity. Each cell in the stack has one select (steering) diode and onenonvolatile nanotube switch. Cells described above with respect to FIGS.43C and 44A-44B use two nanotube elements per cell connected in parallelto increase effective nanotube element thickness. However, with twonanotube elements per cell, it is possible double bit density by storingtwo data states (bits) in the same cell in two nanotube elements thatshare one select (steering) diode without necessarily stacking twoarrays as described further above with respect to FIGS. 33A-33D.

Memory array cross section 4500 illustrated in FIG. 45 shows cell 1 andcell 2 with identical nonvolatile nanotube switches. Since cell 1 andcell 2 are the same, only cell 1 will be described in detail. FIG. 45illustrates cell 1 which stores two bits. One select (steering) diode4525 connects word line WL0 and lower level contact 4530. Cell 1includes the two nonvolatile nanotube switches 4505-1 and 4505-2 bothsharing select (steering) diode 4525.

Nanotube channel element 4570-1 is formed within trench A and is similarto nanotube channel element 4370-3 illustrated in FIG. 43C. Nanotubeelement 4545-1 is in contact with shared lower level contact 4530 andupper level contact 4565-1. Upper level contact 4565-1 is in contactwith bit line BL0-A. Nanotube element 4545-1 may store information viaits resistance state.

Nanotube channel element 4570-2 is formed within trench B. Nanotubeelement 4545-2 is in contact with shared lower level contact 4530 andupper level contact 4565-2. Upper level contact 4565-2 is in contactwith via 4567 which is in contact with bit line BL0-B. Nanotube element4545-2 may also store information via its resistance state.

Cell 1 includes nonvolatile nanotube switch 4505-1 storing one bit, forexample, and nonvolatile nanotube switch 4505-2 also storing one bit,for example such that cell 1 stores two bits, for example. Cross section4500 illustrated in FIG. 45 illustrates a 3D memory array that storestwo bits per cell, one bit in nonvolatile nanotube switch 4505-1 and theother bit in nonvolatile nanotube switch 4505-2. Memory array crosssection 4500 illustrated in FIG. 45 has the same density as stackedarrays shown in FIGS. 33A-33C without requiring the stacking of twoseparate arrays. While this example illustrates anode-on-NT type cells,cathode-on-NT cells may also be used instead.

FIG. 45 illustrates a modified version of FIG. 43C in which sub-minimumupper level contacts 4565-1 and 4565-2 and contact via 4567 are formedusing methods of fabrication corresponding to self aligned spacertechniques, sacrificial shapes, and fill and planarization techniques toform sub-minimum insulator and conductor regions as described furtherabove with respect to FIGS. 36A-36FF. More specifically, self alignedspacer techniques are described further above with respect to FIGS. 36Eand 36F; formation of sub-minimum sacrificial layers is described withrespect to FIGS. 36P through 36S; and formation of minimum andsub-minimum contact regions is described with respect to FIGS. 36Y, 36Z,and 36AA.

FIGS. 33A-33C illustrate two stacked arrays, one cathode-on-NT typearray and the other an anode-on-NT type array to double bit density.Each cell in the stack has one select (steering) diode and onenonvolatile nanotube switch. Cells described above with respect to FIGS.43C and 44A-B use two nanotube elements per cell connected in parallelto increase effective nanotube element thickness. However, with twonanotube elements per cell, it is possible double bit density by storingtwo data states (bits) in the same cell in two nanotube elements thatshare one select (steering) diode without having to stack two arrays asdescribed further above with respect to FIGS. 33A-33C.

Memory array cross section 4600 illustrated in FIG. 46 shows cell 1 andcell 2 with identical nonvolatile nanotube switch configurations. Sincecell 1 and cell 2 are the same, only cell 1 will be described in detail.FIG. 46 illustrates cell 1 which stores two bits, for example. Oneselect (steering) diode 4625 connects word line WL0 and lower levelcontact 4630. Cell 1 includes the two nonvolatile nanotube switches4605-1 and 4605-2 both sharing select (steering) diode 4625.

Nanotube channel element 4670-1 is formed within trench A and is similarto nanotube channel element 4470 illustrated in FIG. 44A. Nanotubeelement 4645-1 is in contact with shared lower level contact 4630 andupper level contact 4665-1. Upper level contact 4665-1 is in contactwith bit line BL0-A. Nanotube element 4645-1 may store information viaits resistance state.

Nanotube element 4645-2 is part of nonvolatile nanotube switch 4605-2which is formed inside cell 1 boundaries as described further above withrespect to nonvolatile nanotube 4468 illustrated in FIG. 44A, except formodified upper level contact structures described further below.Nanotube element 4645-2 is in contact with shared lower level contact4630 and upper level contact 4665-2. Upper level contact 4665-2 is incontact with via 4667 which is in contact with bit line BL0-B. Nanotubeelement 4645-2 may also store information via its resistance state.

Cell 1 includes nonvolatile nanotube switch 4605-1 storing one bit, forexample, and nonvolatile nanotube switch 4605-2 also storing one bit,for example, such that cell 1 stores two bits, for example. Crosssection 4600 illustrated in FIG. 46 illustrates a 3D memory array thatcan store two bits per cell, one bit in nonvolatile nanotube switch4605-1 and the other bit in nonvolatile nanotube switch 4605-2, forexample. Memory array cross section 4600 illustrated in FIG. 46 has thesame density as stacked arrays shown in FIGS. 33A-33C without requiringthe stacking of two separate arrays. While this example illustratesanode-on-NT type cells, cathode-on-NT cells may also be used instead.

FIG. 46 illustrates a modified version of FIGS. 44A-44B in whichsub-minimum upper level contacts 4665-1 and 4665-2 and contact via 4667are formed using methods of fabrication corresponding to self alignedspacer techniques, sacrificial shapes, and fill and planarizationtechniques to form sub-minimum insulator and conductor regions asdescribed further above with respect to FIGS. 36A-36FF. Morespecifically, self aligned spacer techniques are described further abovewith respect to FIGS. 36E and 36F; formation of sub-minimum sacrificiallayers is described with respect to FIGS. 36P through 36S; and formationof minimum and sub-minimum contact regions is described with respect toFIGS. 36Y, 36Z, and 36AA.

Nonvolatile 3D Memory Using Horizontally-Oriented Self-AlignedEnd-Contacted Nanotube Elements Stacked Above Steering (Select) Diodes

FIG. 40 illustrates cross section 4000 and includes nanotube switch 4005in which the thickness of nanotube element 4050 may be equal to the celldimension F. In general, there is no need for the thickness of thenanotube element to be related in any particular way to the lateraldimensions of the cell. In this example, nanotube element 4050 may bedeposited by spray-on methods of fabrication for example. For atechnology node (generation) with F approximately 22 nm and a nanotubeelement thickness of approximately 22 nm for example, the nanotuberegion fills the available cell region. A sidewall contact is eliminatedand Lower level contact 4030 and upper level contact 4065 form the twoterminal (contact) regions to nanotube 4050. Vertical channel lengthL_(SW-CH) is determined by the separation between upper layer contact4065 and lower layer contact 4030. While cross section 4000 achieveshigh levels of 3D cell density, scaling of channel length L_(SW-CH) islimited because nanotube element 4050 is porous. In some embodiments,L_(SW-CH) must maintain a separation of hundreds of nanometers to ensureno shorting occurs between upper level contact 4065 and lower levelcontact 4030 through the nanotube element. However, various methods andconfigurations can be used in order to reduce the thickness of thenanotube element, and thus L_(SW-CH), while still preventing shortingbetween the upper and lower level contacts. Some of exemplary methodsand configurations for achieving this are described in greater detailbelow.

Cross section 4785 illustrated in FIG. 47 shows horizontally-orientednonvolatile nanotube elements separated from upper level contacts andlower level contacts by insulating regions. Nanotube elementend-contacts are used to connect nanotube elements with correspondingupper level contacts on one end and corresponding lower level contactson the other end using trench sidewall wiring. This structure enablescell scaling in nanotube element channel length (L_(SW-CH)), channelwidth (W_(SW-CH)), and height (thickness). Methods of fabrication ofcathode-on-NT 3D memory arrays are described in FIGS. 48A-48BB.

FIG. 49 depicts a nonvolatile nanotube switch using end-contacts. FIG.50 illustrates the operation of the end-contacted nonvolatile nanotubeswitch depicted in FIG. 49.

FIGS. 51 and 52 show cross sections of nanotube element end-contactedswitches used in anode-on-NT 3D memory arrays.

FIGS. 53 and 54A and 54B illustrated a two-high memory stack usingcombinations of cathode-on-NT and anode-on-nanotube 3D memory arraysbased on new 3D cells described in FIGS. 47, 48A-48BB, 51, and 52.

FIGS. 55A-55F illustrate structures and corresponding methods offabrication for trench sidewall wiring formed using conformal conductorsin the trench region. Methods of fabrication used with FIGS. 48A-48BBuse a conductor trench fill approach when forming trench sidewallwiring.

3-Dimensional Cell Structure of Nonvolatile Cells Using NV NT DevicesHaving Vertically Oriented Diodes and Horizontally Oriented Self-AlignedNT Switches Using Conductor Trench-Fill for Cathode-on-NT SwitchConnections

FIG. 47 illustrates cross section 4785 including cells C00 and C01 in a3-D memory embodiment. Nanotube layers are deposited horizontally on aplanar insulator surface above previously defined diode-forming layersas illustrated in FIGS. 34A and 34B shown further above. Self-alignmentmethods, similar to self-alignment methods described further above withrespect to FIGS. 34A-34FF and 36A-36FF, determine the dimensions andlocations of trenches used to define cell boundaries. Self-alignedtrench sidewall wiring connects horizontally-oriented nanotube elementswith vertically-oriented diodes and also with array wiring.

Methods 2710 described further above with respect to FIG. 27A are usedto define support circuits and interconnections 3401.

Next, methods 2730 illustrated in FIG. 27B deposit and planarizeinsulator 3403. Interconnect means through planar insulator 3403 (notshown in cross section 4785 but shown above with respect to crosssection 2800″ in FIG. 28C) may be used to connect metal array lines in3-D arrays to corresponding support circuits and interconnections 3401.By way of example, bit line drivers in BL driver and sense circuits 2640may be connected to bit lines BL0 and BL1 in array 2610 of memory 2600illustrated in FIG. 26A described further above, and in cross section4785 illustrated in FIG. 47. At this point in the fabrication process,methods 2740 may be used to form a memory array on the surface ofinsulator 3403, interconnected with memory array support structure3405-1 illustrated in FIG. 47.

Methods 2740 illustrated in FIG. 27B deposit and planarize metal,polysilicon, insulator, and nanotube elements to form nonvolatilenanotube diodes which, in this example, include multiple verticallyoriented diode and horizontally-oriented nonvolatile nanotube switchseries pairs. Individual cell boundaries are formed in a single etchstep, each cell having a single NV NT Diode defined by a single trenchetch step after layers, except the WL0 layer, have been deposited andplanarized, in order to eliminate accumulation of individual layeralignment tolerances that would substantially increase cell area.Individual cell dimensions in the X direction are F (1 minimum feature)as illustrated in FIG. 47, and also F in the Y direction (not shown)which is orthogonal to the X direction, with a periodicity in X and Ydirections of 2F. Hence, each cell occupies an area of approximately4F².

Vertically-oriented (Z direction) trench sidewall cell wiring on a firstcell sidewall connects a vertically-oriented diode and one end of ahorizontally-oriented nanotube element; and vertically-oriented trenchsidewall cell wiring on a second cell sidewall connects the other end ofthe horizontally-oriented nanotube element with array wiring. Exemplarymethods of forming vertically-oriented trench sidewall cell wiring maybe adapted from methods of patterning shapes on trench sidewalls such asmethods disclosed in U.S. Pat. No. 5,096,849, the entire contents ofwhich are incorporated herein by reference. Horizontally-oriented NV NTswitch element (nanotube element) dimensions in the X and Y directionare defined by trench etching. There are no alignment requirements forthe nanotube elements in the X or Y direction. Nanotube elementthickness (Z direction) is typically in the 5 to 40 nm range. However,nanotube element thickness may be any desired thickness, less than 5 nmor greater than 40 nm for example.

Horizontally-oriented nanotube elements may be formed using a singlenanotube layer, or may be formed using multiple layers. Such nanotubeelement layers may be deposited e.g., using spin-on coating techniquesor spray-on coating techniques, as described in greater detail in theincorporated patent references. FIG. 47 illustrates 3-D memory arraycross section 4785 in the X direction and corresponds to methods offabrication illustrated with respect to FIG. 48. Nanotube element lengthdimension L_(SW-CH) and width dimension W_(SW-CH) are determined byetched trench wall spacing. If trench wall spacing is substantiallyequal to minimum technology node dimension F in both X and Y direction,then for technology nodes 90 nm, 65 nm, 45 nm, and 22 nm for example,L_(SW-CH) and W_(SW-CH) will be approximately 90 nm, 65 nm, 45 nm, and22 nm for example.

Methods fill trenches with an insulator; and then methods planarize thesurface. Then, methods deposit and pattern word lines on the planarizedsurface.

The fabrication of vertically-oriented 3D cells illustrated in FIG. 47proceeds as follows. Methods deposit a bit line wiring layer on thesurface of insulator 3403 having a thickness of 50 to 500 nm, forexample, as described further below with respect to FIG. 48. Fabricationof the vertically-oriented diode portion of structure 4785 is the sameas in FIGS. 34A and 34B described further above and are incorporated inmethods of fabrication described with respect to FIG. 48. Methods etchthe bit line wiring layer and define individual bit lines such as bitline conductors 3410-1 (BL0) and 3410-2 (BL1). Bit lines such as BL0 andBL1 are used as array wiring conductors and may also be used as anodeterminals of Schottky diodes. Alternatively, Schottky diode junctions3418-1 and 3418-2 may be formed using metal or silicide contacts (notshown) in contact with N polysilicon regions 3420-1 and 3420-2, whilealso forming ohmic contacts with bit line conductors 3410-1 and 3410-2,N polysilicon regions 3420-1 and 3420-2 may be doped with arsenic orphosphorus in the range of 10¹⁴ to 10¹⁷ dopant atoms/cm³ for example,and may have a thickness range of 20 nm to 400 nm, for example.

FIG. 47 illustrates a cathode-to-NT type NV NT diode formed withSchottky diodes. However, PN or PIN diodes may be used instead ofSchottky diodes as described further below with respect to FIG. 48A.

The electrical characteristics of Schottky (and PN, PIN) diodes may beimproved (low leakage, for example) by controlling the materialproperties of polysilicon, for example polysilicon deposited andpatterned to form polysilicon regions 3420-1 and 3420-2. Polysiliconregions may have relatively large or relatively small grain boundarysizes that are determined by methods used in the semiconductor regions.For example, SOI deposition methods used in the semiconductor industrymay be used that result in polysilicon regions that are singlecrystalline (no longer polysilicon), or nearly single crystalline, forfurther electrical property enhancement such as low diode leakagecurrents.

Examples of contact and conductors materials include elemental metalssuch as Al, Au, W, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, aswell as metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, othersuitable conductors, or conductive nitrides, oxides, or silicides suchas RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x). Insulators may be SiO₂,SiN_(x), Al₂O₃, BeO, polyimide, Mylar or other suitable insulatingmaterial.

In some cases conductors such as Al, Au, W, Cu, Mo, Ti, and others maybe used as both contact and conductors materials as well as anodes forSchottky Diodes. However, in other cases, optimizing anode material forlower forward voltage drop and lower diode leakage is advantageous.Schottky diode anode materials may be added (not shown) betweenconductors 3410-1 and 3410-2 and polysilicon regions 3420-1 and 3420-2,respectively. Such anode materials may include Al, Ag, Au, Ca, Co, Cr,Cu, Fe, Ir, Mg, Mo, Na, Ni, Os, Pb, Pd, Pt, Rb, Ru, Ti, W, Zn and otherelemental metals. Also, silicides such as CoSi₂, MoSi₂, Pd₂Si, PtSi,RbSi₂, TiSi₂, WSi₂, and ZrSi₂ may be used. Schottky diodes formed usingsuch metals and suicides are illustrated in the reference by NG, K. K.“Complete Guide to Semiconductor Devices”, Second Edition, John Wiley &Sons, 2002m pp. 31-41, the entire contents of which are incorporatedherein by reference.

Next, having completed Schottky diode select devices, methods form N+polysilicon regions 3425-1 and 3425-2 to contact N polysilicon regions3420-1 and 3420-2, respectively, and also to form contact regions forohmic contacts to contacts 3430-1 and 3430-2. N+ polysilicon istypically doped with arsenic or phosphorous to 10²⁰ dopant atoms/cm³,for example, and has a thickness of 20 to 400 nm, for example. N and N+polysilicon region dimensions are defined by trench etching near the endof the process flow.

Next, methods form planar insulating regions 4735-1 and 4735-2 on thesurface of lower level contact (contact) 3430-1 and 3430-2,respectively, typically SiO₂ for example, with a thickness of 20 to 500nm for example and X and Y dimensions defined by trench etching near theend of the process flow.

Next, methods form horizontally-oriented nanotube elements 4740-1 and4740-2 on the surface of insulator regions 4735-1 and 4735-2,respectively, having nanotube element length and width defined by trenchetching near the end of the process flow and insulated from directcontact with lower level contacts 3430-1 and 3430-2, respectively. Inorder to improve the density of cells C00 and C01, nanotube elements4740-1 and 4740-2 illustrated in FIG. 47 are horizontally-oriented withtrench-defined end-contacts 4764 and 4779 in contact with nanotubeelement 4740-1, and end-contacts 4764′ and 4779′ in contact withnanotube element 4740-2 as described further below.Horizontally-oriented nanotube elements and methods of making same aredescribed in greater detail in the incorporated patent references.

Then, methods form protective insulators 4745-1 and 4745-2 on thesurface of conformal nanotube elements 4740-1 and 4740-2, respectively,with X and Y dimensions defined by trench etching near the end of theprocess flow. Exemplary methods of forming protective insulator 4745-1and 4745-2 are described further below with respect to FIG. 48B.

Next, methods form upper level contacts 4750-1 and 4750-2 on the surfaceof protective insulators 4745-1 and 4745-2, respectively, with X and Ydimensions defined by trench etching near the end of the process flow.

Next, methods form (etch) trench openings of width F form innersidewalls of cells C00 and C01 and corresponding upper and lower levelcontacts, nanotube elements, and insulators described further above.

Next, methods form sidewall vertical wiring 4762 and 4762′. Verticalsidewall wiring 4762 forms and connects end-contact 4764 of nanotubeelement 4740-1 with end-contact 4766 of lower level contact 3430-1;vertical sidewall wiring 4762′ forms and connects end-contact 4764′ ofnanotube element 4740-2 with end-contact 4766′ of lower level contact3430-2.

Next, methods complete trench formation (etching) to the surface ofinsulator 3403.

Next, methods fill trench opening with an insulator such as TEOS andplanarize the surface to complete trench fill 4769.

Next, methods form (etch) trench openings of width F that form outersidewalls of cells C00 and C01 and corresponding upper and lower levelcontacts, nanotube elements, and insulators described further above.

Next, methods form sidewall vertical wiring 4776 and 4776′. Verticalsidewall wiring 4776 forms and connects end-contact 4778 of nanotubeelement 4740-1 with the end-contact region of upper level contact4750-1; vertical sidewall wiring 4776′ forms and connects end-contact4778′ of nanotube element 4740-2 with the end-contact region of upperlevel contact 4850-2.

Next, methods complete trench formation (etching) to the surface ofinsulator 3403.

Next, methods fill trench openings with an insulator such as TEOS andplanarize the surface to complete trench fill 4882 and 4882′.

Next, methods directionally etch and form word line contacts 4784C-1 and4784C-2 on the surface of upper level contacts 4750-1 and 4750-2,respectively, by depositing and planarizing a word line layer.

Next, methods pattern word line 4784.

Nonvolatile nanotube diodes forming cells C00 and C01 correspond tononvolatile nanotube diode 1200 in FIG. 12, one in each of cells C00 andC01. Cells C00 and C01 illustrated in cross section 4785 in FIG. 47correspond to corresponding cells C00 and C01 shown schematically inmemory array 2610 in FIG. 26A, and bit lines BL0 and BL1 and word lineWL0 correspond to array lines illustrated schematically in memory array2610.

Methods 2700 illustrated in FIGS. 27A and 27B may be used to fabricatememories using NV NT diode devices with cathode-to-NT switch connectionsfor horizontally-oriented self-aligned NV NT switches such as thoseshown in cross section 4785 illustrated in FIG. 47 as described furtherbelow with respect to FIG. 48. Structures such as cross section 4785 maybe used to fabricate memory 2600 illustrated schematically in FIG. 26A.

Methods of Fabricating 3-Dimensional Cell Structure of Nonvolatile CellsUsing NV NT Devices Having Vertically Oriented Diodes andHorizontally-Oriented Self Aligned NT Switches Using ConductiveTrench-Fill for Cathode-to-NT Switch Connection

Methods 2710 illustrated in FIG. 27A are used to define support circuitsand interconnects similar to those described with respect to memory 2600illustrated in FIG. 26A as described further above. Methods 2710 applyknown semiconductor industry techniques design and fabricationtechniques to fabricated support circuits and interconnections 3401 inand on a semiconductor substrate as illustrated in FIG. 48A. Supportcircuits and interconnections 3401 include FET devices in asemiconductor substrate and interconnections such as vias and wiringabove a semiconductor substrate. FIG. 48A corresponds to FIG. 34Aillustrating a Schottky diode structure, except that an optionalconductive Schottky anode contact layer 3415 shown in FIG. 34A is notshown in FIG. 48A. Note that FIG. 34A′ may be used instead of FIG. 34A′as a starting point if a PN diode structure is desired. If N polysiliconlayer 3417 in FIG. 34A′ were replaced with an intrinsically dopedpolysilicon layer instead (not shown), then a PIN diode would be formedinstead of a PN diode. Therefore, while the structure illustrated inFIG. 48A illustrates a Schottky diode structure, the structure may alsobe fabricated using either a PN diode or a PIN diode.

Methods of fabrication for elements and structures for support circuits& interconnections 3401, insulator 3403, memory array support structure3405, conductor layer 3410, N polysilicon layer 3420, N+ polysiliconlayer 3425, and lower level contact layer 3430 illustrated in FIG. 48are described further above with respect to FIGS. 34A and 34B.

Next, methods of fabrication deposit insulator layer 4835 as illustratedin FIG. 48B on the surface of lower level contact layer 3430. Insulatorlayer 4835 is typically SiO₂ with a thickness range of 20 to 500 nm forexample.

Next, methods deposit a horizontally-oriented nanotube layer 4840 on theplanar surface of insulator layer 4835 as illustrated in FIG. 48B.Horizontally-oriented nanotube layer 4840 may be formed using a singlenanotube layer, or may be formed using multiple nanotube layers. Suchnanotube layers may be deposited e.g., using spin-on coating techniquesor spray-on coating techniques, as described in greater detail in theincorporated patent references.

Next, methods form protective insulator layer 4845 on the surface onnanotube layer 4840 as illustrated in FIG. 48B. Protective insulatorlayer 4845 may be formed using appropriate material known in the CMOSindustry, including, but not limited to: PVDF (Polyvinylidene Fluoride),Polyimide, PSG (Phosphosilicate glass) oxide, Orion oxide, LTO(planarizing low temperature oxide), sputtered oxide or nitride,flowfill oxide, ALD (atomic layer deposition) oxides. CVD (chemicalvapor deposition) nitride may also be used, and these materials may beused in conjunction with each other, e.g., a PVDF layer or mixture ofPVDF and other copolymers may be placed on top of nanotube layer 4840and this complex may be capped with ALD Al₂O₃ layer, however anynon-oxygen containing high temperature polymers could be used aspassivation layers. In some embodiments passivation materials such asPVDF may be mixed or formulated with other organic or dielectricmaterials such as PC7 to generate specific passivation properties suchas to impart extended lifetime and reliability. Various materials andmethods are described in U.S. patent application Ser. No. 11/280,786.

At this point in the fabrication process, methods deposit upper levelcontact layer 4850 on the surface of insulator layer 4845 as illustratedin FIG. 48B. Upper level contact layer 4850 may be 10 to 500 nm inthickness, for example. Upper level contact layer 4850 may be formedusing Al, Au, W, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, as wellas metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides, oxides, or silicides such as RuN,RuO, TiN, TaN, CoSi_(x) and TiSi_(x), for example.

Next methods deposit sacrificial layer 4852 (sacrificial layer 1) onupper level contact layer 4850 as illustrated in FIG. 48C. Sacrificiallayer 4852 may be in the range of 10 to 500 nm thick and be formed usingconductor, semiconductor, or insulator materials such as materialsdescribed further above with respect to lower level contact layer 3430,semiconductor layers 3420 and 3425, and insulator layers 4835 and 4845.

Next, methods deposit and pattern a masking layer (not shown) depositedon the top surface of sacrificial layer 4852 using known industrymethods. The mask opening may be aligned to alignment marks in planarinsulating layer 3403 for example; the alignment is not critical.

Then, methods directionally etch sacrificial layer 4852 to form anopening of dimension DX1 through sacrificial layer 4852 stopping at thesurface of upper level contact layer 4850 using known industry methodsas illustrated in FIG. 48D. Two memory cells that include horizontalnanotube channel elements self aligned and positioned with respect tovertical edges of sacrificial cap 1 region 4852′ and sacrificial cap 1region 4852″ are formed as illustrated further below. The dimension DX1is approximately 3F, where F is a minimum photolithographic dimension.For a 65 nm technology node, DX1 is approximately 195 nm; for a 45 nmtechnology node, DX1 is approximately 135 nm; and for a 22 nm technologynode, DX1 is approximately 66 nm. These DX1 dimensions are much largerthan the technology minimum dimension F and are therefore non-criticaldimensions at any technology node.

Next, methods deposit a second conformal sacrificial layer 4853(sacrificial layer 2) as illustrated in FIG. 48E. The thickness ofconformal sacrificial layer 4853 is selected as F. In this example, if Fis 45 nm, then the thickness of conformal sacrificial layer 4853 isapproximately 45 nm; if F is 22 nm, then the thickness of conformalsacrificial layer 4853 is approximately 22 nm. Conformal sacrificiallayer 4853 may be formed using conductor, semiconductor, or insulatormaterials similar to those materials used to form sacrificial layer 4852described further above.

Next, methods directionally etch conformal sacrificial layer 4853 usingreactive ion etch (RIE) for example, using known industry methods,forming opening 4855 of dimension approximately F, which in this examplemay be in a range of 22 to 45 nm as illustrated in FIG. 48F. The innersidewalls of second sacrificial cap 2 region 4853′ and secondsacrificial cap 2 region 4953″ in opening 4855 are self-aligned to theinner walls of sacrificial regions 4852′ and 4852″ and separated by adistance of approximately F.

At this point in the process, sacrificial regions 4853′ and 4853″ may beused as masking layers for directional etching of trenches using methodsthat define a cell boundary along the X direction for 3D cells using oneNV NT diode with an internal cathode-to-nanotube connection per cell.U.S. Pat. No. 5,670,803, the entire contents of which are incorporatedherein by reference, to co-inventor Bertin, discloses a 3-D array (inthis example, 3D-SRAM) structure with simultaneously trench-definedsidewall dimensions. This structure includes vertical sidewallssimultaneously defined by trenches cutting through multiple layers ofdoped silicon and insulated regions in order avoid multiple alignmentsteps. Such trench directional selective etch methods may cut throughmultiple conductor, semiconductor, and oxide layers as described furtherabove with respect to trench formation in FIGS. 34A-34FF and 36A-36FF.In this example, selective directional trench etch (RIE) removes exposedareas of upper level contact layer 4850 to form upper level contactregions 4850′ and 4850″; removes exposed areas of protective insulatorlayer 4845 to form protective insulator regions 4845′ and 4845″; removesexposed areas of nanotube layer 4840 to form nanotube regions 4840′ and4840″; removes exposed areas of insulating layer 4835 to form insulatingregions 4835′ and 4835″; removes exposed areas of lower level contactlayer 3430 to form lower level contact regions 3430′ and 3430″; andselective directional etch stops on the top surface of N+ polysiliconlayer 3425, forming trench opening 4857 as illustrated in FIG. 48G.

Next, methods such as evaporation or sputtering fill trench 4857 withconductor material 4858 as illustrated in FIG. 48H. Examples ofconductor layer materials are elemental metals such as, Al, Au, W, Cu,Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys suchas TiAu, TiCu, TiPd, PbIn, and TiW, other suitable conductors, orconductive nitrides, oxides, or silicides such as RuN, RuO, TiN, TaN,CoSi_(x) and TiSi_(x). Conductor material is formed into sidewall wiringregions as illustrated further below. Because wiring distances areshort, the sheet resistance of resulting trench sidewall wiring is not aconcern. Nanotube contact resistance values between trench sidewallwiring and the ends of nanotube regions 4840′ and 4840″, nanotubecontact resistance variations, and nanotube contact resistancereliability are useful criteria in selecting conductor type. Nanotuberegions of larger cross sectional areas typically result in loweroverall contact resistance because of multiple parallel nanotubes.Trench sidewall contacts to both nanotube end regions and lower levelmetal sidewall regions are used to form a cell cathode-to-NT connection.A nonvolatile nanotube switch with end-only contacts is describedfurther below with respect to FIGS. 49 and 50.

Next, methods selectively directionally etch conductor 4858 to a depthDZ1 below the top surface of sacrificial cap 2 regions 4853′ and 4853″as illustrated in FIG. 48I. DZ1 is selected to ensure full contact ofnanotube end regions while not contacting upper level contact regions.At this point in the process, the sidewalls of conductor 4858′ are inelectrical contact with one end of nanotube region 4840′ and one end oflower level conductor 3430′, and also in electrical contact with one endof nanotube region 4840″ and one end of lower level conductor 3430″. Twoseparate sidewall wiring regions can be formed as illustrated furtherbelow.

Next, methods deposit a conformal insulator layer 4860 as illustrated inFIG. 48J. Conformal insulator 4860 may be 5 to 50 nm thick, for example,and may be formed from any appropriate known insulator material in theCMOS industry, or packaging industry, for example such as SiO₂, SiN,Al₂O₃, BeO, polyimide, PSG (phosphosilicate glass), photoresist, PVDF(polyvinylidene fluoride), sputtered glass, epoxy glass, and otherdielectric materials and combinations of dielectric materials such asPVDF capped with an Al₂O₃ layer, for example, such as described in U.S.patent application Ser. No. 11/280,786. Insulator 4860 is deposited to afilm thickness that determines the thickness of trench sidewall wiringas described further below.

Next, methods directly etch conformal insulator 4860 using RIE andremove conformal layer material on top horizontal surfaces and bottomhorizontal surfaces at the bottom of trench opening to form trenchopening 4861 with sidewall insulators 4860′ and 4860″ and conductor4858′ as illustrated in FIG. 48K.

Next, methods directionally etch conductor 4858′ using sidewallinsulators 4860′ and 4860″ as masking regions and stop at the topsurface of N+ polysilicon layer 3425 as illustrated in FIG. 48L. Thethickness of sidewall insulators 4860′ and 4860″ determine the thicknessof trench sidewall wiring regions as illustrated below. Trench sidewallwiring 4862 is formed, which forms contact 4864 between trench sidewallwiring 4862 and one end of nanotube region 4840′. Trench sidewall wiring4862 also forms contact 4866 with one sidewall (end) of lower levelcontact 3430′. Trench sidewall wiring 4862′ is formed, which formscontact 4864′ between trench sidewall wiring 4862′ and one end ofnanotube region 4840″. Trench sidewall wiring 4862′ also forms contact4866′ with one sidewall (end) of lower level contact 3430″.

Next, methods directionally etch exposed areas of N+ polysilicon layer3425 to form N+ polysilicon regions 3425′ and 3425″; exposed areas ofpolysilicon layer 3420 to form N polysilicon regions 3420′ and 3420″;and exposed areas of conductor layer 3410 to form conductor regions3410′ and 3410″, stopping at the surface of insulator 3403. Sidewallinsulators 4860′ and 4860″ and trench sidewall conductors 4862 and 4862′are used for masking. Directional etching stops at the top surface ofinsulator 3403 forming trench opening 4867′ as illustrated in FIG. 48M.

Next methods fill trench opening 4867′ with insulator 4869 such as TEOSfor example and planarize as illustrated in FIG. 48N.

At this point in the process, a second cell boundary is formed along theX direction for 3D memory cells. Methods remove (etch) sacrificial caplayer 1 regions 4852′ and 4852″ exposing a portion of the surfaces ofupper level contact region 4850′ and 4850″ as illustrated in FIG. 48O.

At this point in the process, sacrificial regions 4853′ and 4853″ may beused as masking layers for directional etching of trenches using methodsthat define another cell boundary along the X direction for 3D cellsusing one NV NT diode with an internal cathode-to-nanotube connectionper cell as described further above with respect to FIG. 48F. Thisstructure includes vertical sidewalls simultaneously defined by trenchescutting through multiple layers of doped silicon and insulated regionsin order avoid multiple alignment steps. Such trench directionalselective etch methods may cut through multiple conductor,semiconductor, and oxide layers as described further above with respectto trench formation in FIG. 48F and also in FIGS. 34A-34FF and 36A-36FF.In this example, selective directional trench etch (RIE) removes exposedareas of upper level contact regions 4550′ and 4850″ to form upper levelcontacts 4850-1 and 4850-2, respectively; removes exposed areas ofprotective insulator regions 4845′ and 4845″ to form protectiveinsulators 4845-1 and 4845-2, respectively; removes exposed areas ofnanotube regions 4840′ and 4840″ to form nanotube elements 4840-1 and4840-2, respectively; and selective directional etch stops on the topsurface of insulator regions 4835′ and 4835″, forming trench openings4871 and 4871′ as illustrated in FIG. 48P.

Next, methods such as evaporation or sputtering fill trenches 4871 and4871′ with conductor material 4872 as illustrated in FIG. 48Q, and alsodescribed further above with respect to FIG. 48H.

Next, methods selectively directionally etch conductor 4872 to a depthDZ2 below the top surface of sacrificial cap 2 regions 4853′ and 4853″as illustrated in FIG. 48R. DZ2 is adjusted to ensure full contact ofnanotube end regions while also contacting upper level contacts. At thispoint in the process, the sidewalls of conductors 4872′ and 4872″ are inelectrical contact with one end of each of nanotube elements 4840-1 and4840-2, respectively, and one end of upper level conductors 4850-1 and4850-2, respectively. Sidewall wiring regions can be formed, asillustrated further below.

Next, methods deposit a conformal insulator layer 4874 as illustrated inFIG. 48S. Conformal insulator 4874 may be 5 to 50 nm thick, for example,and may be formed from any known insulator material in the CMOSindustry, or packaging industry, for example such as SiO₂, SiN, Al₂O₃,BeO, polyimide, PSG (phosphosilicate glass), photoresist, PVDF(polyvinylidene fluoride), sputtered glass, epoxy glass, and otherdielectric materials and combinations of dielectric materials such asPVDF capped with an Al₂O₃ layer, for example, such as described in U.S.patent application Ser. No. 11/280,786. Insulator 4874 is deposited to afilm thickness that determines the thickness of trench sidewall wiringas described further below.

Next, methods directly etch conformal insulator 4874 using RIE andremove conformal layer material on top horizontal surfaces and bottomhorizontal surfaces at the bottom of trench opening to form trenchopenings with sidewall insulators 4874′ and 4874″ and conductors 4872′and 4872″ as illustrated in FIG. 48T.

Next, methods directionally etch conductors 4872′ and 4872″ usingsidewall insulators 4874′ and 4874″, respectively, and correspondinginsulators on other sides of trenches 4880A and 4880B, respectively,(not shown) as masking regions and stop at the top surface of insulatorregions 4835′ and 4835″, respectively, as illustrated in FIG. 48U. Thethickness of sidewall insulators 4874′ and 4874″ determine the thicknessof trench sidewall wiring regions as illustrated below. Trench sidewallwiring 4876 is formed, which in turn forms contact 4879 between trenchsidewall wiring 4876 and one end of nanotube element 4840-1. Trenchsidewall wiring 4876 also forms contact 4878 with one sidewall (end) ofupper level contact 4850-1. Trench sidewall wiring 4876′ is formed,which in turn forms contact 4879′ between trench sidewall wiring 4876′and one end of nanotube element 4840-2. Trench sidewall wiring 4876′also forms contact 4878′ with one sidewall (end) of upper level contact4850-2.

Next, methods directionally etch exposed areas of insulator regions4835′ and 4835″ to form insulators 4835-1 and 4835-2, respectively;lower level contact regions 3430′ and 3430″ to form lower level contacts3430-1 and 3430-2, respectively; N+ polysilicon regions 3425′ and 3425″to form N+ polysilicon regions 3425-1 and 3425-2, respectively; exposedareas of polysilicon regions 3420′ and 3420″ to form N polysiliconregions 3420-1 and 3420-2; and exposed areas of conductor regions 3410′and 3410″ to form conductors 3410-1 and 3410-2, respectively, stoppingat the surface of insulator 3403. Sidewall insulators 4874′ and 4874″and trench sidewall conductors 4876 and 4876′ are used for masking.Directional etching stops at the top surface of insulator 3403 formingtrench openings 4880A′ and 4880B′ as illustrated in FIG. 48V.

Next methods fill trench openings 4880A′ and 4880B′ with insulator 4882such as TEOS for example and planarize as illustrated in FIG. 48W.

Next, methods remove (etch) sacrificial cap 2 regions 4853′ and 4853″ toform openings 4883 and 4883′, respectively, exposing the top surfaces ofupper level contacts 5850-1 and 5850-2, respectively, as illustrated inFIG. 48X.

Next, methods deposit and planarize a conductor layer 4884 that alsoforms contacts 4884C-1 and 4884C-2 that contact upper level contacts4850-1 and 4850-2, respectively, as illustrated in FIG. 48Y.

Next, conductor layer 4884 is patterned to form word lines orthogonal toconductors (bit lines) 3410-1 and 3410-2 as illustrated further below.

At this point in the process, cross section 4885 illustrated in FIG. 48Yhas been fabricated, and includes NV NT diode cell dimensions of F(where F is a minimum feature size) and cell periodicity 2F defined inthe X direction as well as corresponding array bit lines. Next, celldimensions used to define dimensions in the Y direction are formed bydirectional trench etch processes similar to those described furtherabove with respect to cross section 4885 illustrated in FIG. 48Y.Trenches used to define dimensions in the Y direction are approximatelyorthogonal to trenches used to define dimensions in the X direction. Inthis example, cell characteristics in the Y direction do not requireself alignment techniques described further above with respect to Xdirection dimensions. Cross sections of structures in the Y (bit line)direction are illustrated with respect to cross section X-X′ illustratedin FIG. 48Y.

Next, methods deposit and pattern a masking layer such as masking layer4884A on the surface of word line layer 4884 as illustrated in FIG. 48Z.Masking layer 4884A may be non-critically aligned to alignment marks inplanar insulator 3403. Openings in mask layer 4884A determine thelocation of trench directional etch regions, in this case trenches areapproximately orthogonal to bit lines such as conductor 3410-1 (BL0).

At this point in the process, openings in masking layer 4884A may beused for directional etching of trenches using methods that define newcell boundaries along the Y direction for 3D cells using one NV NT diodewith an internal cathode-to-nanotube connection per cell. All trenchesand corresponding cell boundaries may be formed simultaneously. Thisstructure includes vertical sidewalls simultaneously defined bytrenches. Such trench directional selective etch methods may cut throughmultiple conductor, semiconductor, and oxide layers as described furtherbelow and also described further above with respect to trench formationin FIGS. 48F to 48M and also in FIGS. 34A-34FF and 36A-36FF. In thisexample, selective directional trench etch (RIE) removes exposed areasof conductor layer 4884 to form word line conductors 4884-1 (WL0) and4884-2 (WL1); exposed areas of contact region 4884C-1 to form contacts4884C-1′ and 4884C-1″; exposed areas of upper level contact regions4850-1 and 4850-2 to form upper level contacts 4850-1′ and 4850-1″,removes exposed areas of protective insulator regions 4845-1 and 4845-2to form protective insulators 4845-1′ and 4845-1″; removes exposed areasof nanotube regions 4840-1 and 4840-2 to form nanotube elements 4840-1′and 4840-1″; removes exposed areas of insulator regions 4835-1 and4835-2 to form insulators 4835-1′ and 4835-1″; removes exposed areas oflower level contact regions 3430-1 and 3430-2 to form lower levelcontacts 3430-1′ and 3430-1″; removes exposed areas of N+ polysiliconregions 3425-1 and 3425-2 to form N+ polysilicon regions 3425-1′ and3425-1″; and removes exposed areas of polysilicon regions 3420-1 and3420-2 to form N polysilicon regions 3420-1′ and 3420-1″. Directionaletching stops at the top surface of conductor 3410-1 forming trenchopenings 4886 as illustrated in FIG. 48AA.

Then methods fill trenches 4886 with an insulator 4888 such as TEOS, forexample, and planarize the surface as illustrated by cross section 4885′in FIG. 48BB. Cross section 4885′ illustrated in FIG. 48BB and crosssection 4885 illustrated in FIG. 48Y are two cross sectionalrepresentations of the same 3D nonvolatile memory array with cellsformed with NV NT diode having vertically oriented steering (select)diodes and horizontally-oriented nanotube elements contacted on each endby trench sidewall wiring. Cross section 4885 illustrated in FIG. 48Ycorresponds to cross section 4785 illustrated in FIG. 47.

At this point in the process, cross sections 4885 and 4885′ illustratedin FIGS. 48Y and 48BB, respectively, have been fabricated, nonvolatilenanotube element horizontally-oriented channel length L_(SW-CH) aredefined, including overall NV NT diode cell dimensions of 1F in the Xdirection and 1F in the Y direction, as well as corresponding bit andword array lines. Cross section 4885 is a cross section of two adjacentcathode-to-nanotube type nonvolatile nanotube diode-based cells in the Xdirection and cross section 4885′ is a cross section of two adjacentcathode-to-nanotube type nonvolatile nanotube diode-based cells in the Ydirection.

Cross sections 4885 and 4885′ include corresponding word line and bitline array lines. The nonvolatile nanotube diodes form the steering andstorage elements in each cell illustrated in cross sections 4885 and4885′, and each cell having 1F by 1F dimensions. The spacing betweenadjacent cells is 1F so the cell periodicity is 2F in both the X and Ydirections. Therefore one bit occupies an area of 4F². At the 45 nmtechnology node, the cell area is less than 0.01 um².

Nonvolatile Nanotube Switch with Channel-Region End-Contacted NanotubeElements

FIG. 49 illustrates NV NT Switch 4900 including a patterned nanotubeelement 4910 on insulator 4920 which is supported by substrate 4930.Patterned protective insulator 4935 is in contact with the top surfaceof nanotube element 4910. Examples of nanotube element 4910 andprotective insulator 4935 are described further above with respect toFIGS. 48A-48BB. Terminals (conductor elements) 4940 and 4950 aredeposited adjacent to end-regions of nanotube element 4910 and formterminal-to-nanotube end-region contacts 4960 and 4965, respectively.Examples of end-region contact to nanotube elements are describedfurther above with respect to FIGS. 48L and 48U. The nonvolatilenanotube switch channel length L_(SW-CH) is the separation betweennanotube element end-region contacts 4960 and 4965. Substrate 4930 maybe an insulator such as ceramic or glass, a semiconductor, or an organicrigid or flexible substrate. Insulator 4920 may be SiO₂, SiN, Al₂O₃, oranother insulator material. Terminals (conductor elements) 4940 and 4950may be formed using a variety of contact and interconnect elementalmetals such as Ru, Ti, Cr, Al, Al(Cu), Au, Pd, Ni, W, Cu, Mo, Ag, In,Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu, TiPd, PbIn, andTiW, other suitable conductors, or conductive nitrides, oxides, orsilicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).

Laboratory testing results of individual nonvolatile nanotube switch4900 with nanotube element 4910 channel length of approximately 250 nmand terminals (conductive elements) 4940 and 4950 formed of TiPd areillustrated by graph 5000 in FIG. 50. Nonvolatile nanotube switch 4900switching results for 100 ON/OFF cycles shows that most ON resistancevalues are in range of 10 kOhms to 100 kOhms with a few ON resistancevalues of 800 kOhms as illustrated by resistance values 5010, and OFFresistance values are in the range of 500 MOhms to 100 GOhms asillustrated by resistance values 5020. In a few cases 5030, ONresistance values were greater than 100 MOhms.

If a 3D memory array is used in a nonvolatile Flash memory application,Flash architecture could be used to detect cases 5030 of ON resistancevalues that are greater than OFF resistance values 5010 and apply one orseveral additional cycles as needed to ensure ON resistance values ofless than 1 MOhm as illustrated by graph 5000.

Nonvolatile nanotube switch 4900 ON/OFF resistance values demonstrate alowering of the spread of ON resistance values and a tighter ONresistance value distribution after several tens (or hundreds) ofcycles. Graphs 5010 and 5020 in the 80 to 100 ON/OFF cycle range show ONresistance values between 10 kOhms and less than 1 MOhms, for example,and OFF resistance values greater than 80 MOhms. Such nonvolatilenanotube switches may be used in any memory architecture. Applying tensor hundreds of cycles to as-fabricated nonvolatile nanotube switches4900 may be used as part of a memory array burn-in operation. Examplesof applied voltages and currents resulting in cycling between ON and OFFresistance values is described further above with respect to FIGS. 11Aand 11B.

3-Dimensional Cell Structure of Nonvolatile Cells Using NV NT DevicesHaving Vertically Oriented Diodes and Horizontally Oriented Self AlignedNT Switches Using Conductor Trench-Fill for Anode-on-NT SwitchConnections

FIG. 51 illustrates cross section 5185 including cells C00 and C10 in a3-D memory embodiment. Nanotube layers are deposited horizontally on aplanar insulator surface above previously defined diode-forming layersas illustrated in FIGS. 36A and 36B shown further above. Self-alignmentmethods, similar to self-alignment methods described further above withrespect to FIGS. 34A-34FF, 36A-36FF, and 48A-48BB determine thedimensions and locations of trenches used to define cell boundaries.Self-aligned trench sidewall wiring connects horizontally-orientednanotube elements with vertically-oriented diodes and also with arraywiring.

Methods 3010 described further above with respect to FIG. 30A are usedto define support circuits and interconnections 3601.

Next, methods 3030 illustrated in FIG. 30B deposit and planarizeinsulator 3603. Interconnect means through planar insulator 3603 (notshown in cross section 5185 but shown above with respect to crosssection 2800″ in FIG. 28C) may be used to connect metal array lines in3-D arrays to corresponding support circuits and interconnections 3601.By way of example, word line drivers in WL driver and sense circuits2930 may be connected to word lines WL0 and WL1 in array 2910 of memory2900 illustrated in FIG. 29A described further above, and in crosssection 5185 illustrated in FIG. 51. At this point in the fabricationprocess, methods 3040 may be used to form a memory array on the surfaceof insulator 3603, interconnected with memory array support structure3605-1 illustrated in FIG. 51.

Exemplary methods 3040 illustrated in FIG. 30B deposit and planarizemetal, polysilicon, insulator, and nanotube elements to form nonvolatilenanotube diodes which, in this example, include multiple verticallyoriented diode and horizontally-oriented nonvolatile nanotube switchseries pairs. Individual cell boundaries are formed in a single etchstep, each cell having a single NV NT Diode defined by a single trenchetch step after layers, except the BL0 layer, have been deposited andplanarized, in order to eliminate accumulation of individual layeralignment tolerances that would substantially increase cell area.Individual cell dimensions in the Y direction are F (1 minimum feature)as illustrated in FIG. 51, and also F in the X direction (not shown)which is orthogonal to the Y direction, with a periodicity in X and Ydirections of 2F. Hence, each cell occupies an area of approximately4F².

Vertically-oriented (Z direction) trench sidewall cell wiring on a firstcell sidewall connects a vertically-oriented diode and one end of ahorizontally-oriented nanotube element; and vertically-oriented trenchsidewall cell wiring on a second cell sidewall connects the other end ofthe horizontally-oriented nanotube element with array wiring. Exemplarymethods of forming vertically-oriented trench sidewall cell wiring maybe adapted from methods of patterning shapes on trench sidewalls such asmethods disclosed in U.S. Pat. No. 5,096,849. Horizontally-oriented NVNT switch element (nanotube element) dimensions in the X and Y directionare defined by trench etching. There are no alignment requirements forthe nanotube elements in the X or Y direction. Nanotube elementthickness (Z direction) is typically in the 5 to 40 nm range. However,nanotube element thickness may be any desired thickness, less than 5 nmor greater than 40 nm for example.

Horizontally-oriented nanotube elements may be formed using a singlenanotube layer, or may be formed using multiple layers. Such nanotubeelement layers may be deposited e.g., using spin-on coating techniquesor spray-on coating techniques, as described in greater detail in theincorporated patent references. FIG. 51 illustrates 3-D memory arraycross section 5185 in the Y direction and corresponds to methods offabrication illustrated with respect to FIGS. 48A-48BB, but with a smallmodification in that FIGS. 36A and 36B replace FIGS. 34A and 34B inorder to form an anode-on-NT 3D memory cell (instead of a cathode-on-NTmemory cell). NV NT switches are formed using the same methods offabrication as the methods of fabrication as described further abovewith respect to FIGS. 48A-48BB. Nanotube element length dimensionL_(SW-CH) and width dimension W_(SW-CH) are determined by etched trenchwall spacing. If trench wall spacing is equal to minimum technology nodedimension F in both X and Y direction, then for technology nodes 90 nm,65 nm, 45 nm, and 22 nm for example, L_(SW-CH) and W_(SW-CH) will beapproximately 90 nm, 65 nm, 45 nm, and 22 nm for example.

Methods fill trenches with an insulator; and then methods planarize thesurface. Then, methods deposit and pattern bit lines on the planarizedsurface.

The fabrication of vertically-oriented 3D cells illustrated in FIG. 51proceeds as follows. Methods deposit a word line wiring layer on thesurface of insulator 3603 having a thickness of 50 to 500 nm, forexample, as described further above with respect to FIGS. 48A-48BB (theword line wiring layer in FIG. 51 corresponds to the bit line wiringlayer in FIGS. 48A-48BB). Fabrication of the vertically-oriented diodeportion of structure 5185 is the same as in FIGS. 36A and 36B describedfurther above and are incorporated in methods of fabrication describedwith respect to FIG. 51. Methods etch the word line wiring layer anddefine individual word lines such as word line conductors 3610-1 (WL0)and 3610-2 (WL1). Word lines such as WL0 and WL1 are used as arraywiring conductors and may also be used as contacts to N+ regions 3620-1and 3620-2, which are in contact with N regions 3625-1 and 3625-2forming Schottky diode cathodes. N+ polysilicon regions 3620-1 and3620-2 may be doped with arsenic or phosphorous of 10²⁰ or greater, andN polysilicon regions 3625-1 and 3625-2 may be doped with arsenic orphosphorus in the range of 10¹⁴ to 10¹⁷ dopant atoms/cm³ for example,and may have a thickness range of 20 nm to 400 nm, for example.

FIG. 51 illustrates an anode-to-NT type NV NT diode formed with Schottkydiodes. However, PN or PIN diodes may be used instead of Schottkydiodes.

The electrical characteristics of Schottky (and PN, PIN) diodes may beimproved (low leakage, for example) by controlling the materialproperties of polysilicon, for example polysilicon deposited andpatterned to form polysilicon regions 3625-1 and 3625-2. Polysiliconregions may have relatively large or relatively small grain boundarysizes that are determined by methods used in the semiconductor regions.For example, SOI deposition methods used in the semiconductor industrymay be used that result in polysilicon regions that are singlecrystalline (no longer polysilicon), or nearly single crystalline, forfurther electrical property enhancement such as low diode leakagecurrents.

Methods form lower level contacts 3630-1 and 3630-2. Examples of contactconductor materials include elemental metals such as Al, Au, W, Cu, Mo,Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys such asTiAu, TiCu, TiPd, PbIn, and TiW, other suitable conductors, orconductive nitrides, oxides, or silicides such as RuN, RuO, TiN, TaN,CoSi_(x) and TiSi_(x). Insulators may be SiO₂, SiN_(x), Al₂O₃, BeO,polyimide, Mylar or other suitable insulating material.

Lower level contacts 3630-1 and 3630-2 also form anodes of Schottkydiodes having Schottky diode junctions 3618-1 and 3618-2. In some casesconductors such as Al, Au, W, Cu, Mo, Ti, and others may be used as bothcontact conductor materials as well as anodes for Schottky Diodes.However, in other cases, optimizing anode material for lower forwardvoltage drop and lower diode leakage is advantageous. Schottky diodeanode materials may be added (not shown) between lower level contacts(and Schottky diode anodes) 3630-1 and 3630-2 and polysilicon regions3625-1 and 3625-2, respectively. Such anode materials may include Al,Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo, Na, Ni, Os, Pb, Pd, Pt, Rb, Ru,Ti, W, Zn and other elemental metals. Also, silicides such as CoSi₂,MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂, and ZrSi₂ may be used. Schottkydiodes formed using such metals and silicides are illustrated in thereference by NG, K. K. “Complete Guide to Semiconductor Devices”, SecondEdition, John Wiley & Sons, 2002m pp. 31-41, the entire contents ofwhich are incorporated herein by reference.

Next, methods form planar insulating regions 4735-1 and 4735-2 on thesurface of lower level contact (contact) 3630-1 and 3630-2,respectively, typically SiO₂ for example, with a thickness of 20 to 500nm for example and X and Y dimensions defined by trench etching near theend of the process flow.

Next, methods form horizontally-oriented nanotube elements 4740-1 and4740-2 on the surface of insulator regions 4735-1 and 4735-2,respectively, having nanotube element length and width defined by trenchetching near the end of the process flow and insulated from directcontact with lower level contacts 3430-1 and 3430-2, respectively. Inorder to maximize the density of cells C00 and C10, nanotube elements4740-1 and 4740-2 illustrated in FIG. 51 are horizontally-oriented withtrench-defined end-contacts 4764 and 4779 contacting nanotube element4740-1, and end-contacts 4764′ and 4779′ contacting nanotube element4740-2 as described further below Horizontally-oriented nanotubeelements are described in greater detail in the incorporated patentreferences.

Then, methods form protective insulators 4745-1 and 4745-2 on thesurface of conformal nanotube elements 4740-1 and 4740-2, respectively,with X and Y dimensions defined by trench etching near the end of theprocess flow. Exemplary methods of forming protective insulator 4745-1and 4745-2 are described further above with respect to FIG. 48B.

Next, methods form upper level contacts 4750-1 and 4750-2 on the surfaceof protective insulators 4745-1 and 4745-2, respectively, with X and Ydimensions defined by trench etching near the end of the process flow.

Next, methods form (etch) trench openings of width F form innersidewalls of cells C00 and C10 and corresponding upper and lower levelcontacts, nanotube elements, and insulators described further above.

Next, methods form sidewall vertical wiring 4762 and 4762′. Verticalsidewall wiring 4762 forms and connects end-contact 4764 of nanotubeelement 4740-1 with end-contact 4766 of lower level contact 3630-1;vertical sidewall wiring 4762′ forms and connects end-contact 4764′ ofnanotube element 4740-2 with end-contact 4766′ of lower level contact3630-2.

Next, methods complete trench formation (etching) to the surface ofinsulator 3403.

Next, methods fill trench opening with an insulator such as TEOS andplanarize the surface to complete trench fill 4769.

Next, methods form (etch) trench openings of width F that form outersidewalls of cells C00 and C10 and corresponding upper and lower levelcontacts, nanotube elements, and insulators described further above.

Next, methods form sidewall vertical wiring 4776 and 4776′. Verticalsidewall wiring 4776 forms and connects end-contact 4779 of nanotubeelement 4740-1 with the end-contact region 4778 of upper level contact4750-1; vertical sidewall wiring 4776′ forms and connects end-contact4779′ of nanotube element 4740-2 with the end-contact region 4778′ ofupper level contact 4850-2.

Next, methods complete trench formation (etching) to the surface ofinsulator 3403.

Next, methods fill trench openings with an insulator such as TEOS andplanarize the surface to complete trench fill 4882 and 4882′.

Next, methods directionally etch and form bit line contacts 5184C-1 and5184C-2 on the surface of upper level contacts 4750-1 and 4750-2,respectively, by depositing and planarizing a bit line layer.

Next, methods pattern bit line 5184.

Nonvolatile nanotube diodes forming cells C00 and C10 correspond tononvolatile nanotube diode 1300 in FIG. 13, one in each of cells C00 andC10. Cells C00 and C10 illustrated in cross section 5185 in FIG. 51correspond to corresponding cells C00 and C10 shown schematically inmemory array 2910 in FIG. 29A, and word lines WL0 and WL1 and bit lineBL0 correspond to array lines illustrated schematically in memory array2910.

After the fabrication of cross section 5185 illustrated in FIG. 51, 3Dmemory cell boundaries in the X direction are formed by simultaneouslytrench etching, trench filling with an insulator and planarizing. Bitlines and bit line contacts to upper level contacts are then formed tocomplete cross section 5185′ in FIG. 52 that corresponds to crosssection 5185 in FIG. 51.

Cross section 5185′ illustrated in FIG. 52 illustrates support circuitsand interconnections 3601 and insulator 3603 as described further abovewith respect to FIG. 51. Cross section 5185′ is in the X direction alongword line WL0.

N+ polysilicon regions 3620-1′ and 3620-1″ form contacts between wordline 3610-1 (WL0) and N polysilicon 3625-1′ and 3625-1″, respectively,that form diode cathode regions. Lower level contacts 3430-1′ and3430-1″ act as anodes to form Schottky diode junctions 3618-1′ and3618-1″ as well as contacts to nanotube elements 4840-1′ and 4840-1″,respectively. Contacts between nanotube elements and lower levelcontacts are illustrated in corresponding cross section 5185 in FIG. 51.

Insulator 4835-1′ and 4835-1″ is used to separate nanotube elements4840-1′ and 4840-1″ from electrical contact with lower level contacts3630-1′ and 3630-1″, respectively.

Protective insulators 4845-1′ and 4845-1″ provide a protecting regionabove the nanotube elements, and also electrically separate nanotubeselements 4840-1′ and 4840-1″ from electrical contact with upper levelcontacts 4850-1′ and 4850-1″, respectively. Contacts between nanotubeelements and upper level contacts are illustrated in corresponding crosssections 5185.

Bit line contacts 5184-1′ and 5184-1″ connect upper level contacts4850-1′ and 4850-1″, respectively, to bit lines 5184-1 (BL0) and 5184-2(BL1), respectively.

Corresponding cross sections 5185 and 5185′ illustrated in FIGS. 51 and52, respectively, show an anode-to-NT 3D memory array withhorizontally-oriented nanotube elements. Nanotube channel length andchannel width (W_(SW-CH)) correspond to NV NT diode cell dimensions of1F in the X direction and 1F in the Y direction, as well ascorresponding bit and word array lines. Cross section 5185 is a crosssection of two adjacent anode-to-nanotube type nonvolatile nanotubediode-based cells in the Y direction and cross section 5185′ is a crosssection of two adjacent anode-to-nanotube type nonvolatile nanotubediode-based cells in the X direction. Cross sections 5185 and 5185′include corresponding word line and bit line array lines. Thenonvolatile nanotube diodes form the steering and storage elements ineach cell illustrated in cross sections 5185 and 5185′, and each cellhas 1F by 1F dimensions. The spacing between adjacent cells is 1F so thecell periodicity is 2F in both the X and Y directions. Therefore one bitoccupies an area of 4F². At the 45 nm technology node, the cell area isless than 0.01 um².

Corresponding cross sections 5185 and 5185′ illustrated in FIGS. 51 and52 methods of fabrication correspond to the methods of fabricationdescribed with respect to FIGS. 48A-48BB, except that the verticalposition of N polysilicon and N+ silicon layers are interchanged. NV NTswitch fabrication methods of fabrication are the same. The onlydifference is that the N polysilicon layer is etched before N+polysilicon layer when forming trenches in cross sections 5185 and5185′.

Nonvolatile Memories Using NV NT Diode Device Stacks with bothAnode-to-NT Switch Connections and Cathode-to-NT Switch Connections andHorizontally-Oriented Self Aligned End-Contacted NV NT Switches

FIG. 32 illustrates a method 3200 of fabricating embodiments having twomemory arrays stacked one above the other and on an insulating layerabove support circuits formed below the insulating layer and stackedarrays, and with communications means through the insulating layer.While method 3200 is described further below with respect to nonvolatilenanotube diodes 1200 and 1300, method 3200 is sufficient to cover thefabrication of many of the nonvolatile nanotube diode embodimentsdescribed further above. Note also that although methods 3200 aredescribed in terms of 3D memory embodiments, methods 3200 may also beused to form 3D logic embodiments based on NV NT diodes arranged aslogic arrays such as NAND and NOR arrays with logic support circuits(instead of memory support circuits) as used in PLAs, FPGAs, and PLDs,for example.

FIG. 53 illustrates a 3D perspective drawing 5300 that includes atwo-high stack of three dimensional arrays, a lower array 5302 and anupper array 5304. Lower array 5302 includes nonvolatile nanotube diodecells C00, C01, C10, and C11. Upper array 5304 includes nonvolatilenanotube diode cells C02, C12, C03, and C13. Word lines WL0 and WL1 areoriented along the X direction and bit lines BL0, BL1, BL2, and BL3 areoriented along the Y direction and are approximately orthogonal to wordlines WL1 and WL2. Nanotube element channel length L_(SW-CH) is orientedhorizontally as shown in 3D perspective drawing 5300. Cross sections ofcells C00, C01, C02 and C03 are illustrated further below in FIG. 54Aand cells C00, C02, C12, and C10 are illustrated further below in FIG.54B.

In general, methods 3210 fabricate support circuits and interconnectionsin and on a semiconductor substrate. This includes NFET and PFET deviceshaving drain, source, and gate that are interconnected to form memory(or logic) support circuits. Such structures and circuits may be formedusing known techniques that are not described in this application. Someembodiments of methods 3210 are used to form a support circuits andinterconnections 5401 layer as part of cross sections 5400 and 5400′illustrated in FIGS. 54A and 54B using known methods of fabrication inand on which nonvolatile nanotube diode control and circuits arefabricated. Support circuits and interconnections 5401 are similar tosupport circuits and interconnections 3401 illustrated in FIGS. 47 and3601 illustrated in FIG. 51, for example, but are modified toaccommodate two stacked memory arrays. Note that while two-high stackedmemory arrays are illustrated in FIG. 54, more than two-high 3D arraystacks may be formed (fabricated), including but not limited to 4-highand 8 high stacks for example.

Next, methods 3210 are also used to fabricate an intermediate structureincluding a planarized insulator with interconnect means and nonvolatilenanotube array structures on the planarized insulator surface such asinsulator 5403 illustrated in cross sections 5400 and 5400′ in FIGS. 54Aand 54B, respectively, and are similar to insulator 3403 illustrated inFIG. 47 and insulator 3601 illustrated in FIG. 51, but are modified toaccommodate two stacked memory arrays. Interconnect means includevertically-oriented filled contacts, or studs, for interconnectingmemory support circuits in and on a semiconductor substrate below theplanarized insulator with nonvolatile nanotube diode arrays above and onthe planarized insulator surface. Planarized insulator 5403 is formedusing methods similar to methods 2730 illustrated in FIG. 27B.Interconnect means through planar insulator 5403 (not shown in crosssection 5400) are similar to contact 2807 illustrated in FIG. 28C andmay be used to connect array lines in first memory array 5410 and secondmemory array 5420 to corresponding support circuits and interconnections5401. Support circuits and interconnections 5401 and insulator 5403 formmemory array support structure 5405-1.

Next, methods 3220, similar to methods 2740, are used to fabricate afirst memory array 5410 using diode cathode-to-nanotube switches basedon a nonvolatile nanotube diode array similar to a nonvolatile nanotubediode array cross section 4785 illustrated in FIG. 47 and correspondingmethods of fabrication.

Next, methods 3230 similar to methods 3040 illustrated in FIG. 30B,fabricate a second memory array 5420 on the planar surface of firstmemory array 5410, but using diode anode-to-nanotube switches based on anonvolatile nanotube diode array similar to a nonvolatile nanotube diodearray cross section 5185 illustrated in FIG. 51 and correspondingmethods of fabrication

FIG. 54A illustrates cross section 5400 including first memory array5410 and second memory array 5420, with both arrays sharing word line5430 in common. Word lines such as 5430 are defined (etched) during amethods trench etch that defines memory array (cells) when forming array5420. Cross section 5400 illustrates combined first memory array 5410and second memory array 5420 in the word line, or X direction, withshared word line 5430 (WL0), four bit lines BL0, BL1, BL2, and BL3, andcorresponding cells C00, C01, C02, and C03. The array periodicity in theX direction is 2F, where F is a minimum dimension for a technology node(generation).

FIG. 54B illustrates cross section 5400′ including first memory array5410′ and second memory array 5420′ with both arrays sharing word lines5430′ and 5432 in common. Word line 5430′ is a cross sectional view ofword line 5430. Word lines such as 5430′ and 5432 are defined (etched)during a trench etch that defines memory array (cells) when formingarray 5420′. Cross section 5400′ illustrates combined first memory array5410′ and second memory array 5420′ in the bit line, or Y direction,with shared word lines 5430′ (WL0) and 5432 (WL1), two bit lines BL0 andBL2, and corresponding cells C00, C10, C02, and C12. The arrayperiodicity in the Y direction is 2F, where F is a minimum dimension fora technology node (generation).

The memory array cell area of 1 bit for array 5410 is 4F² because of the2F periodicity in the X and Y directions. The memory array cell area of1 bit for array 5420 is 4F² because of the 2F periodicity in the X and Ydirections. Because memory arrays 5420 and 5410 are stacked, the memoryarray cell area per bit is 2F². If four memory arrays (not shown) arestacked, then the memory array cell area per bit is 1F².

In some embodiments, methods 3240 using industry standard fabricationtechniques complete fabrication of the semiconductor chip by addingadditional wiring layers as needed, and passivating the chip and addingpackage interconnect means.

In operation, memory cross section 5400 illustrated in FIG. 54A andcorresponding memory cross section 5400′ illustrated in FIG. 54Bcorrespond to the operation of memory cross section 3305 illustrated inFIG. 33B and corresponding memory cross section 3305′ illustrated inFIG. 33B′. Memory cross section 5400 and corresponding memory crosssection 5400′ operation is the same as described with respect towaveforms 3375 illustrated in FIG. 33D.

Method of Forming Trench Sidewall Wiring Using Conformal ConductorDeposition as an Alternative to Trench Fill

FIG. 48G illustrates a trench opening 4857 that is then filled withconductor 4858 as illustrated in FIG. 48H. Trench sidewall wiring isthen formed as further illustrated in methods of fabrication describedin FIG. 48A-48BB.

Conformal conductor deposition may be used instead of a trench fillconductor to create trench sidewall wiring as illustrated in FIGS.55A-55F. Exemplary methods of fabrication illustrated in FIGS. 55A-55Fare based on an adaptation of U.S. Pat. No. 5,096,849 illustrated inFIGS. 41A-41B.

Some methods deposit a conformal conductor layer 5510 in opening 4857(FIG. 48G) as illustrated in FIG. 55A and forms trench opening 5515.Examples of conductors layer materials are elemental metals such as, Al,Au, W, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metalalloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides, oxides, or silicides such as RuN,RuO, TiN, TaN, CoSi_(x) and TiSi_(x). Conductor material is formed intosidewall wiring regions as illustrated further below. Because wiringdistances are short, the sheet resistance of resulting trench sidewallwiring is not a concern.

Next, methods fill trench opening 5515 with sacrificial material 5520 asillustrated in FIG. 55B. Sacrificial material 5520 may be a conductor,semiconductor, or an insulator. If an insulator is selected, sacrificialmaterial 5520 may be formed from any known insulator material in theCMOS industry, or packaging industry, for example such as SiO₂, SiN,Al₂O₃, BeO, polyimide, PSG (phosphosilicate glass), photoresist, PVDF(polyvinylidene fluoride), sputtered glass, epoxy glass, and otherdielectric materials.

Next, methods etch (RIE) sacrificial material 5520 to a depth DZ10 belowthe bottom of upper level contacts 4850′ and 4850″ as illustrated inFIG. 55C leaving sacrificial material 5520′.

Next, methods remove (etch) exposed regions of the conformal trenchsidewall conductor using known industry methods as illustrated in FIG.55D and leaving sacrificial material 5520′.

Next, methods remove (etch) remaining sacrificial material 5520′ usingknown industry methods as illustrated in FIG. 55E.

Next, methods RIE remaining conformal conductor forming trench sidewallwiring 5535 and 5535′. Then, methods directionally etch remainingsemiconductor and metal layers to form trench sidewall wiring 5535 and5535′ corresponding to sidewall wiring 4862 and 4862′ in FIG. 48L, andforming trench 5550.

Methods of fabrication using conformal conductor deposition instead ofconductor trench fill as described with respect to FIGS. 55A-55F may beapplied to methods of fabrication described with respect to FIGS.48A-48BB to form 3D memory cross section 4885 illustrated in FIG. 48Yand 3D memory cross section 4885′ illustrated in FIG. 48BB.

Methods of fabrication using conformal conductor deposition as describedwith respect to FIGS. 55A-55F may also be used to form 3D memory crosssection 5185 illustrated in FIG. 51 and 3D memory cross section 5185′illustrated in FIG. 52.

Nonvolatile Nanotube Blocks

Nonvolatile nanotube switches (NV NT Switches) are described in detailin U.S. patent application Ser. No. 11/280,786, and switch examples andoperation are summarized briefly in this application as illustrated inFIGS. 3-11B illustrated above. FIGS. 3-6B illustratehorizontally-oriented NV NT switches 300, 400, 500, and 600, and FIG. 7Billustrate vertically-oriented NV NT switch 750. These switches areformed by nanotube elements of thickness in the range of 0.5 to 10 nm,for example, that are contacted by metallic terminals in contact withsurface regions at opposite ends of the patterned nanotube elements.

FIGS. 26A and 29A illustrate nonvolatile nanotube diode-based memoryarrays and circuits using cathode-on-NT and anode-on-NT type nonvolatilenanotube diodes, respectively, as described further above with respectto FIGS. 12 and 13. It is desirable to fabricate the densest possiblememory arrays at each technology node F, where F is the minimumtechnology node lithographic dimension. If each cell is F×F andseparated by a dimension F from adjacent cells, then the cell-to-cellperiodicity is 2F and the minimum cell area for a technology node F is4F². If individual cells can hold more than one bit, or if arrays can bestacked one above the other, then the effective memory cell may be 2F²or 1F², for example.

FIG. 28C illustrates cross section 2800″ in which the NV NT diode cellincludes a vertically-oriented diode steering (select) device in contactwith a horizontally-oriented nanotube which is larger than a minimumfeature size F in the X direction because horizontally-placed nanotubeelement contacts at opposite ends of nanotube element 2850 extend beyondminimum feature F. FIGS. 28A and 28B, as well as 31A, 31B, and 31C showvertically-oriented nanotubes with bottom and side/top contacts that arecompatible with minimum feature size F.

However, even with vertically-oriented nanotubes, scaling to smalldimensions such as technology node F=22 nm (or smaller) may in someembodiments be limited by the nanotube fabric density of the nanotubeelement, that is the number of individual nanotubes available in thewidth direction of the device. Another way to express nanotube fabricdensity is to measure the size of void regions as illustrated in FIG.38. FIG. 39 illustrates nanotube elements of increased thickness inorder to increase the number of nanotubes available for a device ofminimum feature width F, which may be 45 nm, 35 nm, or 22 nm forexample. FIG. 40 illustrates a dense memory cell in which a nanotubeelement 4050 has a cross section F×F. The nanotube thickness determinesthe channel length L_(SW-CH), which is defined by the separation betweenupper level contact 4065 and lower level contact 4030 of nanotube switch4005. Upper level contacts may also be referred to as top contacts andlower level contacts may also be referred to as bottom contacts. Thickernanotube elements such as nanotube element 4050 may be referred to as anonvolatile nanotube blocks. NV NT diode arrays fabricated using NVnanotube blocks such as nanotube element 4050 with upper level and lowerlevel contacts as illustrated further above in FIG. 40, and illustratedfurther below with respect to FIGS. 57, 67 and 68, result in arelatively simple self aligned three-dimensional NV memory arraystructures.

Nonvolatile nanotube blocks (“NV NT blocks”) can be thought of asnanotube elements that include 3-D volumes of nanotube fabric. The termNV NT blocks is used to distinguish relatively thick nanotube elementsfrom relatively thin nanotube elements, e.g., those illustrated in FIGS.3-7B. For example, NV NT blocks may have thicknesses ranging, e.g., fromabout 10 nm to 200 nm (or more), e.g., from about 10 to 50 nm. Thus, thethickness of the block is generally substantially larger than thediameters of individual nanotubes in the block, e.g., at least about tentimes larger than the individual nanotube diameters, forming a 3-Dvolume of nanotubes. In contrast, some other kinds of nanotube elementsare relatively thin, for example having about the same thickness as thenanotube diameters themselves (e.g., approximately 1 nm), forming amonolayer. In many cases, relatively thin elements can be considered tobe “2-D” in nature (although at the nanoscopic level 3-D features can ofcourse be seen). In general, both relatively thin nanotube fabrics, andrelatively thick NV NT blocks (e.g., over a broad range of thicknesses,such as from less than about 1 nm to 200 nm or more) include a networkof nanotubes.

In many embodiments, NV NT blocks are shaped, sized, and/or aresufficiently dense such that terminals may contact the blocks on anysurface(s), including the bottom, top, side, and end, or in anycombination of surfaces. The size and/or density of the fabric thatforms the block substantially prevents the terminals from contactingeach other through the fabric and shorting. In other words, the sizeand/or density of the fabric physically separates the terminals from oneanother. As discussed above relative to FIG. 38, one way of ensuringthat the fabric forming the NV NT block is sufficiently dense is tocontrol the distribution of the size of voids within the fabric. Asdiscussed in greater detail below, the density of the fabric of the NVNT block can be controlled by selecting appropriate depositionparameters. For example, the nanotubes forming the fabric can be denselydeposited using spray coating techniques, or by using spin-coating tocoat multiple layers on top of each other. Or, as described in greaterdetail below, thinner layers may be formed by incorporating asacrificial material into the nanotube fabric, for example either duringor after the deposition of the nanotube fabric. This sacrificialmaterial substantially prevents the terminals from coming into contactwhen the terminals are formed, i.e., physically separates the terminals.The sacrificial material can later be substantially removed, leavingbehind the nanotube fabric. The nanotube fabric need not be as dense orthick as in other embodiments, because the terminals are already formedwith a given physical separation from each other.

In many embodiments, many of the nanotubes within the nanotube fabricforming the NV NT block lie substantially parallel to the surface onwhich they are disposed. In some embodiments, for example if thenanotubes are spin-coated onto a surface, at least some of the nanotubesmay also generally extend laterally in a given direction, although theirorientation is not constrained to that direction. If another layer ofnanotubes is spin-coated on top of that layer, the nanotubes maygenerally extend in the same direction as the previous layer, or in adifferent direction. Additionally, while many the nanotubes of theadditional layer will also be generally parallel to the surface, some ofthe nanotubes may curve downwards to fill voids in the previous nanotubelayer. In other embodiments, for example if the nanotubes arespray-coated onto a surface, the nanotubes will still lie generallyparallel to the surface on which they are disposed, although they mayhave generally random orientations relative to each other in the lateraldirection. In other embodiments, the nanotubes may extend randomly inall directions.

In many embodiments, NV NT blocks have a thickness or height that is onthe order of one or more of its lateral dimensions. For example, asdescribed in greater detail below, one or more dimensions of the NV NTblock can be defined lithographically, and one dimension defined by theas-deposited thickness of the nanotube fabric forming the NV NT block.The lithographically defined dimension(s) scale with the technology node(F), enabling the fabrication of devices with minimum lateral dimensionsof approximately F. e.g., of about 65 nm for F=65 nm, of about 45 nm forF=45 nm, of about 32 nm for F=32 nm, of about 22 nm for F=22 nm, orbelow. For example, for F=22 nm, an NV NT block could have dimensions ofabout 22 nm×22 nm×35 nm, assuming that the nanotube fabric forming theNV NT block is about 35 nm thick. Other dimensions and thicknesses arepossible. Depending on the arrangement of the terminals, and thethickness and as-deposited characteristics of the nanotube fabricforming the NV NT block, the distance between the terminals (i.e., theswitch channel length) may be defined either by a lithographicallydefined dimension of the NV NT block. Alternately, the distance betweenthe terminals may be defined by the thickness of the fabric forming theNV NT block, which in some circumstances may be sub-lithographic.Alternately, the switch channel length may be defined by providing theterminals in an arrangement that is not directly related to a dimensionof the NV NT block itself, but rather by patterning the terminals tohave features that are separated from each other by a particulardistance. In general, as illustrated in greater detail below, NV NTblocks enable the fabrication of switching elements with areas at leastdown to about 1F².

Note that a “NV NT block” need not be cube-shaped, e.g., a volume havingall dimensions approximately equal, or even have parallel sides,although some embodiments will have those features. For example, incertain embodiments, shapes defined in masking layers at minimumdimensions may have rounded corners such that square shapes as-drawn maybe approximately circular as-fabricated, or may be generally square butwith rounded features. An approximately circular masking layer resultsin an approximately cylindrical nonvolatile nanotube element that isalso referred to as a NV NT block in this invention. Therefore, nanotubeelement 4050 illustrated by cross section 4000 in FIG. 40 may have anas-fabricated square cross section F×F if the masking layer used todefine trench boundaries is an F×F square as illustrated further belowin FIG. 57A. Alternatively, nanotube element 4050 illustrated in crosssection 4000 may have an as-fabricated approximately circular crosssection of diameter approximately F as part of a cylindrical NV NT blockelement as illustrated further below in FIG. 57A′.

Individual NT-to-NT overlap regions are estimated to be between 0.5×0.5nm to 10×10 nm in size, which is below available SEM resolutionlimitations. FIG. 3 illustrates a NV NT switch 300 that corresponds toNV NT switch 600/600′ illustrated in FIGS. 6A and 6B. With respect toFIG. 6A, NV NT Switch 600 is in an ON state such that voltage applied toterminal 620 is transmitted to terminal 610 by patterned nanotubeelement 630 with a NV NT network in an electrically continuous ON stateas illustrated by SEM voltage contrast imaging. FIG. 6B illustrates NVNT Switch 600′, which corresponds to NV NT Switch 600, but is in an OFFstate. In an OFF state, patterned nanotube element 630 forms a NV NTnetwork in an electrically discontinuous state, and does notelectrically connect terminals 610 and 620. SEM voltage contrast imagingof NV NT Switch 600′ in FIG. 6B illustrates patterned nanotube element630 in which patterned nanotube element region 630′ is electricallyconnected to terminal 620 (light region) and patterned nanotube elementregion 630″ is electrically connected to terminal 610′ (dark region),but where patterned nanotube element regions 630′ and 630″ are notelectrically connected to each other. Terminal 610′ is dark sincevoltage applied to terminal 620 does not reach terminal 610′ because ofthe electrical discontinuity in the NV NT network between patternednanotube element regions 630′ and 630″. Note that terminal 610′ is thesame as terminal 610, except that it is not electrically connected toterminal 620 in NV NT Switch 600′. While the electrical NV NT networkdiscontinuity is visible in terms of the light portion of region 630′and the dark portion of region 630′, individual nanoscale NV NT switchesforming the NV NT network are not visible due to SEM resolutionlimitations.

In operation, as illustrated further above in FIGS. 9A-9B and with testvoltages and timings illustrated in FIGS. 11A-11B, switch 300 switchesbetween ON and OFF states. In the ON state, the resistance measuredduring the read operation is near-ohmic. NV NT elements fabricated witha variety of thicknesses and terminal (contact) configurationsillustrated further above with respect to FIGS. 49 and 50, and furtherbelow with respect to FIGS. 56A-65, exhibit electrical switchingcharacteristics similar to those in FIGS. 9A-9B when test conditionssimilar to those illustrated in FIGS. 11A-11B are applied. Nanotubeelement switching appears relatively insensitive to geometricalvariations, with the possible exception of lower voltage operation atshorter switch channel lengths L_(SW-CH) as illustrated in FIG. 10.

FIGS. 56A-56F and 57A-57C further below illustrate various relativelythin NV nanotube elements and relatively thick NV nanotube elements (NVNT blocks) with various terminal contact location configurations in3-dimensional perspective.

FIGS. 58A-65 illustrate nonvolatile switches fabricated using variousnonvolatile nanotube elements and corresponding measured electricalswitching characteristics. These nonvolatile nanotube elements andterminal contact configurations correspond to those illustrated in FIGS.56A-56F and 57A-57C.

FIGS. 66A-66C illustrate various methods of fabrication of a variety ofnonvolatile nanotube blocks, such as those illustrated in FIGS. 40, 47,49, 56A-56F, 57A-57C, and 58A-65.

FIGS. 67 and 68A-68I illustrate structures and methods of fabricatingthe memory cell described further above with respect to cross section4000 illustrated in FIG. 40. FIGS. 67 and 68A-68I are described withrespect to cathode-on-NT NV NT diode configurations. FIGS. 69 and 70illustrate structures of memory cells based on anode-to-NT NV NT diodeconfigurations.

FIGS. 71 and 72A-72B illustrate 2-high stacked arrays of 3-D NV NTdiode-based cells that include shared array lines such as shared wordlines. FIGS. 73 and 74 illustrate 2-high stacked arrays of 3-D NV NTdiode-based cells that do not share array lines such as shared wordlines.

FIGS. 75 and 76A-76D illustrate 3-D NV NT diode-based structures andcorresponding simplified methods of fabrication. Simplified methods offabrication enable multi-level arrays of 4, 8, 16 and higher number oflevels as illustrated in a perspective drawing illustrated in FIG. 77.

NV NT Switches Fabricated with Nonvolatile Nanotube Blocks, VariousTerminal Locations, and Switching Characteristics Thereof

NV NT switch 5600A illustrated in 3-D perspective drawing in FIG. 56Ashows a NV NT switch with relatively thin (e.g., about 0.5 to less than10 nm) nonvolatile nanotube element 5602A and top contact locations5605A and 5607A. Contact locations illustrate where terminals (notshown) contact the surface of nanotube element 5602A. NV NT switch 5600Acorresponds to NV NT switch 300 illustrated in FIG. 3, where nanotubeelement 5602A corresponds to nanotube element 330, contact location5605A corresponds to the location of terminal 310, and contact location5607A corresponds to the location of terminal 320.

NV NT switch 5600B illustrated in 3-D perspective drawing in FIG. 56Bshows a NV NT switch with thin nonvolatile nanotube element 5602B andbottom contact locations 5605B and 5607B. Contact locations illustratewhere terminals (not shown) contact the surface of nanotube element5602B. NV NT switch 5600B corresponds to NV NT switch 500 illustrated inFIG. 5, where nanotube element 5602B corresponds to nanotube element530, contact location 5605B corresponds the location of terminal 510,and contact location 5607B corresponds to the location of terminal 520.

NV NT switch 5600C illustrated in 3-D perspective drawing in FIG. 56Cshows a NV NT switch with thin nonvolatile nanotube element 5602C andtop contact location 5605C and bottom contact location 5607C. Contactlocations illustrate where terminals (not shown) contact the surface ofnanotube element 5602B. NV NT switch 5600C combines top and bottomcontacts to the same nanotube element.

NV NT switch 5600D illustrated in 3-D perspective drawing in FIG. 56Dshows a NV NT switch with NV NT block (thick NV NT element) 5610 andcontact locations 5612 and 5614. NV NT switch 5600D corresponds to NV NTswitch 5800/5800′/5870 having structure and electrical switching resultsdescribed further below with respect to FIGS. 58A-58D and 59,respectively. In the illustrated embodiment, corresponding switch 5800is scaled to the technology node used to lithographically define itslateral dimensions. For example, a technology node F=22 nm can provide aswitch channel length of approximately 22 nm, and a width ofapproximately 22 nm for this embodiment. As discussed above, in manyembodiments it is desirable to fabricate the switch channel length to beas small as possible, e.g., as small as the technology node allows,although in other embodiments larger channel lengths may be desirable.The thickness of the NV NT block defines the height of the switch 5600D,which in certain embodiments is approximately 10 nm, although otherthicknesses are possible as discussed elsewhere. Contact location 5612in FIG. 56D includes side contact locations 5612-1 and 5612-2, a topcontact location 5612-3, and an end contact location (not visible), andcorresponds to contacts 5830-1 and 5830-2 in FIGS. 58A-58D. Contactlocation 5614 includes side contact location 5614-1, a second sidecontact location (not visible), top contact location 5614-2, and endcontact 5614-3, and corresponds to contacts 5840-1 and 5840-2.

NV NT switch 5600E illustrated in 3-D perspective drawing in FIG. 56Eshows a NV NT switch with NV NT block 5620 and end-contact locations5622 and 5625. NV NT block 5620 corresponds to nanotube element 4910,end-contact location 5622 corresponds to end-region contact 4965, andend-contact location 5625 corresponds to end-region contact 4960illustrated further above with respect to NV NT switch 4900 illustratedin FIG. 49. Switch operation is illustrated in FIG. 50. Also asdescribed further below with respect to NV NT switch 6000/6000′/6050illustrated in FIGS. 60A-60C, NV NT block 5620 corresponds to nanotubeelement 6010, end-contact location 5622 corresponds to end-regioncontact 6040, and end-contact location 5625 corresponds to end-regioncontact 6030. Electrical switching characteristics are described withrespect to FIG. 61.

NV NT switch 5600F illustrated in 3-D perspective drawing in FIG. 56Fshows a NV NT switch with NV NT block 5630, bottom contact location5632, and combined end-contact location 5634 including combinedend-contact location 5634-1 and top contact location 5634-2. NV NTswitch 5600F corresponds to NV NT switch 6200/6200′ described furtherbelow with respect to FIGS. 62A-62B. NV NT block 5630 corresponds to NVNT block 6210, bottom contact location 5632 corresponds to bottomcontact 6230, and combined end contact location 5634-1 and top contactlocation 5634-2 correspond to combined end contacts 6240-1 and 6240-2,respectively. Electrical switching characteristics are described withrespect to FIG. 63A-63B.

NV NT switch 5700A illustrated in 3-D perspective drawing in FIG. 57Ashows a NV NT switch with NV NT block 5710 and bottom contact location5715 and top contact location 5720. NV NT switch 5700A corresponds to NVNT switch 6400/6400′/6450 having structure and electrical switchingresults described further below with respect to FIGS. 64A-64C and 65,respectively. NV NT block 5710 corresponds to NV NT block 6410, bottomcontact location 5715 corresponds to bottom contact 6427, and topcontact location 5720 corresponds to top contact 6437 illustrated inFIG. 64B. Switching results for switch 6400 illustrate no topcontact-to-bottom contact shorting though NV NT block at a giventhickness, e.g., 35 nm.

NV NT switch 5700A also corresponds to nanotube element 4050 illustratedin FIG. 40 if an F×F masking layer is used in the fabrication. NV NTswitch 5700A′ illustrated in a 3-D perspective drawing in FIG. 57A′ isformed with an approximately round masking layer of diameter F caused bycorner-rounding of the drawn image in the masking layer as describedfurther above. NV NT block 5710′ is approximately cylindrical in shapewith a circular cross section of approximate diameter F, bottom contactlocation 5715′ and top contact location 5720′. The corresponding dioderegion in cross section 4000 is formed at the same time as nanotubeelement 4050 and may have a square cross section F×F or a circular crosssection of approximately F in diameter. In other words, the 3-D NV NTdiode forming the storage cell in cross section 4000 forms a stack witha NV NT block switch on top of a steering (select) diode, with the stackapproximately square or approximately circular in cross section shape.

Void regions sufficiently small in size and number as described furtherabove with respect to nanotube layer 3800 illustrated in FIG. 38 can beused in the fabrication of NV NT block 6410 illustrated in FIGS. 64A-64Cfurther below without shorts between bottom contact 5425 and top contact6435 separated by a given distance, e.g., approximately 35 nm. NV NTblock 6410 corresponds to NV NT block 5710 in the 3-D perspectiveillustration in FIG. 57A.

FIG. 57B illustrated in a 3-D perspective drawing shows NV NT switch5700B in which block 5730 has smaller separation of bottom contactlocation 5735 and top contact location 5740 than the correspondingseparation between corresponding contact locations illustrated in FIG.57A. The block volume is also shaded indicating that it is fabricateddifferently than block 5710. Fabrication differences will be describedfurther below with respect to FIGS. 66A-66C. However, a brief summary ofsignificant differences is given. NV NT blocks described with respect toFIGS. 56A-56F, FIG. 57A and FIG. 57A′, and corresponding figuresdescribed further above, can be fabricated using carbon nanotubesdeposited from CMOS compatible, trace metal free standard dispersions inaqueous or non-aqueous solvents as described in greater detail in theincorporated patent references. Such nanotube element layers may bedeposited using spin-on coating techniques or spray-on coatingtechniques. Block 5730 illustrated in FIG. 57B may be fabricated with asacrificial polymer, for example polypropylene carbonate, dissolved inan organic solvent such as NMP or cyclohexanone described further belowwith respect to FIGS. 66A-66C. Top terminals are formed in contact withtop contact region 5740. The presence of the sacrificial polymer in theNV NT block 5730 structure enables top and bottom contacts to befabricated in relatively close proximity, e.g., less than about 35 nm,for example about 22 nm or less, e.g., about 10 nm (e.g., about 10-22nm). After patterning and insulation, the sacrificial polymer(polypropylene carbonate, for example), is evaporated, through aninsulating layer, or prior to insulating, leaving substantially noresidue, at evaporation temperatures in the range of 200 to 400 deg. C.for example. NV NT switch 5700B′ illustrated in FIG. 57B′ shows block5730′ after sacrificial polymer material removal (e.g., afterevaporation), and with bottom contact region 5735′ and top contactregion 5740′. NV NT block 5730B′ is similar to NV NT block 5700A, exceptthat top and bottom contact regions may be more closely spaced.

FIG. 57C illustrated in a 3-D perspective drawing shows NV NT switch5700C in which NV NT block 5750 includes a shaded region indicating thatNV NT block 5750 includes additional material between individualnanotubes as described further below with respect to FIGS. 66A-66C.Bottom contact region 5755 formed prior to NV NT block 5750 deposition,and top contact region 5760 is formed after NV NT block 5750 deposition.This additional material may enhance performance characteristics of NVNT block 5750. Such additional material may be a polymer such aspolypropylene carbonate that is not evaporated and remains as part NV NTblock 5750 structure. Alternatively, polypropylene carbonate may havebeen evaporated as illustrated in FIG. 57B′ and the NV NT block 5730′then filled with a porous dielectric material prior to top contactformation to enhance the switching properties of NV NT switch 5700C.

NV NT Switches Fabricated with Nonvolatile Nanotube Block DimensionsScaled to the Technology Node

FIG. 58A illustrates a top view of NV NT Switch 5800 and FIG. 58Billustrates cross section 5800′ corresponding to cross section Z1-Z1′shown in FIG. 58A. In certain embodiments, nonvolatile nanotube block5810 on substrate 5820 has an overall length of approximately 800 nm, awidth of approximately 24 nm, and a thickness of approximately 10 nm. Asdiscussed above, cross section dimensions are typically determined bythe technology node, however, thickness dimensions orthogonal to thecross section may not correspond to the technology node. Terminal 5825contacts NV NT block 5810 at end-contact (end-region contact) 5830-1 andtop contact 5830-2. Side contacts (not shown) are also used asillustrated in a corresponding 3-D illustration in FIG. 56D. Terminal5835 contacts NV NT block 5810 at end-contact 5840-1 and top contact5840-2. Side contacts (not shown) are also used as illustrated in acorresponding 3-D illustration in FIG. 56D. NV NT switch 5800/5800′channel length L_(SW-CH) is determined by the separation of terminals5825 and 5835, which is approximately 22 nm for example. Switch channelwidth W_(SW-CH) is approximately 24 nm for example, and is determined byetching. Film thickness H_(SW-CH) is approximately 10 nm as deposited,for example. The electrical performance of block 5810 is determined inpart by a NV NT network contained in a volume of approximately 22 nm(L_(SW-CH))×24 nm (W_(SW-CH))×10 nm (H_(SW-CH)), in some embodiments,and corresponds to a NV NT switch formed with a NV NT block scaled to atechnology node F of 22 nm. In this example, terminals 5825 and 5835 areformed using Ti/Pd, however, terminals may be formed using a variety ofcontact and interconnect elemental metals such as Ru, Ti, Cr, Al,Al(Cu), Au, Pd, Pt, Ni, Ta, W, Cu, Mo, Ag, In, Ir, Pb, Sn, as well asmetal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides, oxides, or silicides such as RuN,RuO, TiN, TaN, CoSi_(x) and TiSi_(x). Substrate 5820 may be an insulatorsuch as ceramic or glass, a semiconductor with an insulated surface, ametal with an insulated surface, or an organic rigid or flexiblesubstrate.

FIG. 58C illustrates a SEM image of an exemplary nonvolatile nanotubeswitch 5850 prior to passivation and corresponds to nonvolatile nanotubeswitches 5800/5800′ illustrated in FIGS. 58A and 58B. Nonvolatilenanotube switch 5850 includes NV NT block 5855 corresponding to NV NTblock 5810, terminal 5860 corresponding to terminal 5825, terminal 5865corresponding to terminal 5835, and substrate 5868 corresponding tosubstrate 5820. Nonvolatile nanotube switch 5850 has been fabricatedwith terminal-to-terminal channel length L_(SW-CH) of 21.9 nm, channelwidth W_(SW-CH) of 24.4 nm as illustrated in FIG. 58C, and thickness ofapproximately 10 nm (not shown in FIG. 58C). FIG. 58D illustrates an SEMimage of nanotube layer 5875 used to form NV NT block 5855. Nanotubelayer 5875 was deposited using 18 spin-on depositions of nanotubes in anaqueous solvent and had a four point probe resistance measured value of150 ohms. The SEM of nanotube layer 5875 cannot resolve individualnanotubes, which typically have diameters in the range of about 0.5 nmto about 10 nm depending on nanotube type such as SWNTs, DWNTs, andMWNTs, or a mix thereof. Nanotubes in the SEM image appear much largerthan their actual diameters. Nanotube layer 5875 was formed using bothsemiconducting and metallic-type nanotubes.

Laboratory testing results of nonvolatile nanotube switch 5850 isillustrated by graph 5900 illustrated in FIG. 59. Nonvolatile nanotubeswitch 5850 switching results for 100 ON/OFF cycles shows that most ONresistance values 5910 are in a range of 50 kOhms to 75 kOhms, and OFFresistance values 5920 are greater than 500 MOhms. Laboratory testingwas similar to testing described further above with respect to FIGS.11A-11B.

NV NT Switches Fabricated with Nonvolatile Nanotube Blocks with EndContacts

FIG. 60A illustrates a top view of NV NT Switch 6000 and FIG. 60Billustrates cross section 6000′ corresponding to cross section Z2-Z2′shown in FIG. 60A that includes NV NT block 6010 with only end contacts.Nonvolatile nanotube block 6010 on substrate 6020 also includes aprotective insulator 6015. In an illustrative embodiment, protectiveinsulator 6015 is an SiO₂ oxide of thickness 100 nm and 250 nm by 250 nmin size, although in general other dimensions and insulating materialsmay be used. Protective insulator 6015 can be used as a masking layer topattern NV NT block 6010 to desired dimensions, e.g., 250×250 nm lateraldimension in the illustrated embodiment. NV NT 6010 has a giventhickness, e.g., approximately 50 nm. Terminal 6025 contacts NV NT block6010 at end-contact (end-region contact) 6030. Terminal 6035 contacts NVNT block 6010 at end-contact 6040. In the embodiments illustrated inFIGS. 60A and 60B, NV NT switch channel length L_(SW-CH) and W_(SW-CH)are directly related to the lateral dimensions of NV NT block 6010,e.g., both are approximately 250 nm using the example block dimensionsprovided above. Terminals 6025 and 6035 overlap protective insulator6015 as fabricated, however, the overlap region has substantially noeffect on electrical operation. NV NT switch 5600E is a 3-Drepresentation in FIG. 56E corresponding to NV NT switch 6000/6000′ inFIGS. 60A and 60B, with NV NT switch 5620 corresponding to NV NT block6010. The electrical performance of block 6010 is determined by a NV NTnetwork contained in the volume of the block, e.g., approximately 250 nm(L_(SW-CH))×250 nm (W_(SW-CH))×50 nm (H_(SW-CH)), using the exampledimensions provided above. In this example, terminals 6025 and 6035 areformed using Ti/Pd, however, terminals may be formed using a variety ofcontact and interconnect elemental metals such as Ru, Ti, Cr, Al,Al(Cu), Au, Pd, Pt, Ni, Ta, W, Cu, Mo, Ag, In, Ir, Pb, Sn, as well asmetal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides, oxides, or silicides such as RuN,RuO, TiN, TaN, CoSi_(x) and TiSi_(x). Substrate 6020 may be an insulatorsuch as ceramic or glass, a semiconductor with an insulated surface, ametal with an insulated surface, or an organic rigid or flexiblesubstrate.

FIG. 60C illustrates a SEM image of nonvolatile nanotube switch 6050prior to passivation and corresponds to nonvolatile nanotube switch6000/6000′ illustrated in FIGS. 60A and 60B. Nonvolatile nanotube switch6050 includes NV NT block 6010 (not visible in this top view), exposedportion of protective insulator 6055 corresponding to protectiveinsulator 6015, terminal 6065 and overhang region 6060 corresponding toterminal 6025, terminal 6075 and overhang region 6070 corresponding toterminal 6035, and substrate 6080 corresponding to substrate 6020.Nonvolatile nanotube switch 6050 has been fabricated withterminal-to-terminal channel length L_(SW-CH) of approximately 250 nm,channel width W_(SW-CH) of approximately 250 nm, and a thickness ofapproximately 50 nm (not shown in FIG. 60C).

NV NT switch 6000/6000′ corresponds to NV NT switch 4900 describedfurther above with respect to FIG. 49 but providing more details on theNV NT switch structure, including an SEM image. NV NT block 6010corresponds to nanotube element 4910, protective insulator 6015corresponds to protective insulator 4935, terminals 6025 and 6035correspond to terminals 4940 and 4950, respectively, except thatterminals 6025 and 6035 also include regions that overlap protectiveinsulator 6015. End contacts (end-region contacts) 6030 and 6040correspond to end-region contacts 4960 and 4965, respectively, andsubstrate 6020 corresponds to a combination of insulator 4920 andsubstrate 4930.

Laboratory ON/OFF switching test results of nanotube switch 6050 withonly end-region contacts corresponds to the electrical characteristicsof NV NT switch 4900 described further above with respect to graph 5000illustrated in FIG. 50. Nonvolatile nanotube switch 4900 switchingresults for 100 ON/OFF cycles shows that most ON resistance values arein range of 10 kOhms to 100 kOhms with a few ON resistance values of 800kOhms as illustrated by resistance values 5010, and OFF resistancevalues are in the range of 500 MOhms to 100 GOhms as illustrated byresistance values 5020. In a few cases 5030, ON resistance values weregreater that 100 MOhms. I-V characteristics of NV NT switch 6050 in theON state are illustrated by graph 6100 in FIG. 61 showing a near-ohmicON resistance behavior.

NV NT Switches Fabricated with Nonvolatile Nanotube Blocks with Bottomand End/Top Contacts

FIG. 62A illustrates a top view of NV NT Switch 6200 and FIG. 62Billustrates cross section 6200′ corresponding to cross section Z3-Z3′shown in FIG. 62A. In one embodiment, nonvolatile nanotube block 6210 onsubstrate 6220 has dimensions of approximately 100×80 nm in crosssection and 50 nm high, although other dimensions are possible. Bottomterminal 6225 forms bottom contact 6230 and terminal 6235 forms combinedend contact 6240-1 and top contact 6240-2. Bottom contact 6230 and topcontact 6240-2 overlap by approximately 150 nm. NV NT switch 6200channel length L_(SW-CH) is not well defined in this configurationbecause of the placement of terminals 6225 and 6235 contacts to NV NTblock 6210. Switch 6200 is illustrated in a corresponding 3-Dperspective drawing in FIG. 56F, where NV NT block 5630 corresponds toNV NT block 6210, bottom contact location 5632 corresponds to bottomcontact 6225, end contact location 5634-1 corresponds to end contact6240-1, and top contact location 5634-2 corresponds to top contact6240-2. In this example, terminals 6225 and 6235 are formed using Ti/Pd,however, terminals may be formed using a variety of contact andinterconnect elemental metals such as Ru, Ti, Cr, Al, Al(Cu), Au, Pd,Pt, Ni, Ta, W, Cu, Mo, Ag, In, Ir, Pb, Sn, as well as metal alloys suchas TiAu, TiCu, TiPd, PbIn, and TiW, other suitable conductors, orconductive nitrides, oxides, or silicides such as RuN, RuO, TiN, TaN,CoSi_(x) and TiSi_(x). Substrate 6220 may be an insulator such asceramic or glass, a semiconductor with an insulated surface, a metalwith an insulated surface, or an organic rigid or flexible substrate.

Laboratory ON/OFF switching test results of nanotube switch 6200/6200′are described with respect to graph 6300 illustrated in FIG. 63A andgraph 6350 illustrated in FIG. 63B. Test conditions are similar to thosedescribed further above with respect to FIGS. 11A-11B; write 0corresponds to erase, and write 1 corresponds to program. Graph 6300tests apply one write 0 voltage pulse of 6 volts, one write 1 voltagepulse of 6 V, and measure ON resistance at each ON/OFF cycle for 100cycles. ON resistance values 6310 are in the 120 kOhm to 1 MOhm rangeand OFF resistance values 6320 are above 100 MOhms. In two cases, ONresistance values 6330 exceeded 1 GOhm indicating failure to switch tothe ON state. Graph 6350 tests apply one write 0 voltage pulse of 6volts, five write 1 voltage pulses of 6 V, and measure ON resistance ateach ON/OFF cycle for 100 cycles. ON resistance values 6360 are in the130 kOhm to 1 MOhm range and OFF resistance values 6370 are above 800MOhms. In one case, ON resistance values 6380 exceeded 1 GOhm indicatingfailure to switch to the ON state.

NV NT Switches Fabricated with Nonvolatile Nanotube Blocks with Top andBottom Contacts

FIG. 64A illustrates a top view of NV NT Switch 6400 and FIG. 64Billustrates cross section 6400′ corresponding to cross section Z4-Z4′shown in FIG. 64A of a NV NT block 6410 with top and bottom contacts.Nonvolatile nanotube block 6410 is formed on the surface of insulator6415, which is on substrate 6420, and overlaps bottom terminal 6425embedded in insulator 6415 to form bottom contact 6427. Bottom terminal6425 is formed with Ti/Pd of thickness 25 nm. Horizontal dimensions ofterminal 6425 are not critical. NV NT block 6410 can be etched from alarger nanotube structure 6410′. In one embodiment, insulator 6430 is anSiO₂ oxide approximately 50 nm thick of approximate width W_(INSUL) of200 nm and overlaps a portion of nanotube structure 6410′. Otherembodiments may have other suitable insulators, of other suitabledimensions. Top terminal 6435 of approximate width W_(TOP CONTACT) of,for example, 100 nm, overlaps a portion of insulator 6430 and extendsbeyond insulator 6430 to overlap a portion of nanotube structure 6410′beyond the edge of insulator 6430 to form a top contact region 6440having dimensions C1 and C2 and forming top contact 6437. Exposedregions of nanotube structure 6410′ outside the boundaries 6445 definedby top terminal 6435, insulator 6430, and nanotube structure 6410′ areetched using nanotube etching techniques described in incorporatedpatent references to form NV NT block 6410. ON/OFF switching of NV NTblock 6410 occurs mostly in a region defined by dimensions C1 and C2 intop contact region that forms top contact 6437 above bottom contact6427. Top contact 6437 and bottom contact 6427 are separated by thethickness of the NV NT block 6410, which in one example is approximately35 nm, although other thicknesses are possible. In one embodiment, C1 isapproximately in the range of 40 to 80 nm and C2 is approximately 100nm. The portion of NV NT network that switches between ON and OFF statesis mostly between top and bottom contacts 6437 and 6427, respectively,within approximate dimensions, for example of about 100×40×35 nm volumeof NV NT block 6410 (some dimensions not visible in FIGS. 64A-64C) usingthe illustrative dimensions provided above. The channel length L_(SW-CH)is the distance between top and bottom contacts of approximately 35 nm,in one embodiment. NV NT switch 5700A illustrated in FIG. 57A is a 3-Drepresentation corresponding to NV NT switch 6400/6400′ in FIGS. 64A and64B, with NV NT block 5710 corresponding to NV NT block 6410. Bottomcontact location 5715 corresponds to bottom contact 6427 and top contactlocation 6720 corresponds to top contact 6437. The electricalperformance of block 6410 is determined by a NV NT network mostlycontained in a volume of approximately 100 nm×40 nm×35 nm as describedfurther above, using the illustrative dimensions. In this example,terminals 6425 and 6435 are formed using Ti/Pd, however, terminals maybe formed using a variety of contact and interconnect elemental metalssuch as Ru, Ti, Cr, Al, Al(Cu), Au, Pd, Pt, Ni, Ta, W, Cu, Mo, Ag, In,Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu, TiPd, PbIn, andTiW, other suitable conductors, or conductive nitrides, oxides, orsilicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x). Insulators6415 6430 may be SiO₂, AL₂O₃, SiN, polyimide, and other compatibleinsulator materials. Substrate 6420 may be an insulator such as ceramicor glass, a semiconductor with an insulated surface, a metal with aninsulated surface, or an organic rigid or flexible substrate.

FIG. 64C illustrates a SEM image of nonvolatile nanotube switch 6450just prior to final etch and passivation and corresponds to nonvolatilenanotube switch 6400/6400′ illustrated in FIGS. 64A and 64B. Final etchdefines the block 6410 dimensions. Nonvolatile nanotube switch 6450 isshown just prior to NV NT block 6410 formation, exposed portion ofinsulator 6455 corresponding to insulator 6415, nanotube structure 6460prior to final etch corresponding to nanotube structure 6410′, insulator6465 corresponding to insulator 6430, top terminal 6470 corresponding totop terminal 6435, and top contact region 6475 corresponding to topcontact region 6440. Nonvolatile nanotube switch 6450 has beenfabricated with a channel length L_(SW-CH) of approximately 35 nmcorresponding to the thickness of the NV NT block between top and bottomcontacts.

A graph 6500 of nonvolatile nanotube switch 6450 switching results for100 ON/OFF cycles is illustrated in FIG. 65. ON resistance values 6510show that most ON resistance values are in range of 100 kOhms to 1 MOhm,and OFF resistance values 6520 are approximately 1 GOhm or higher. Thetest conditions are similar to those described further above withrespect to FIG. 11; write 0 corresponds to erase and write 1 correspondsto program. Graph 6500 illustrated in FIG. 65 used one 7 volts write 0pulse, five 6 volts write 1 pulses, and switched the NV NT switchbetween ON and OFF states for 100 cycles. No shorting betweenoverlapping top and bottom contacts was observed.

NV NT switches using NV NT blocks as switching elements demonstrateON/OFF switching for fabricated devices over a wide range of horizontaldimensions, e.g., from 22 nm to 300 nm and contacting schemes involvingbottom, top, end, and side contacts in various combinations. NV NTblocks may be used in various integration schemes to form a largevariety of three-dimensional nonvolatile nanotube diode-based memoryarrays. For example, cross section 4000 illustrated in FIG. 40 shows aNV NT block, referred to as nanotube element 4050, with a top contactreferred to as upper level contact 4065 and a bottom contact referred toas lower level contact 4030, forming nonvolatile nanotube switch 4005.Cross section 4785 illustrated in FIG. 47 shows NV NT blocks with endcontacts, referred to as nanotube elements 4740-1, with end contacts4779 and 4764, and nanotube elements 4740-2 with end contacts 4779′ and4764′.

The flexibility of NV NT blocks enables integration in a variety ofstructures and product applications. For example, NV NT switches formedusing NV NT blocks may be used as scalable nonvolatile nanotube switchesin structures and circuits, such as the structures and circuitsdescribed in U.S. Provisional Patent Application No. 60/836,343. Also,NV NT switches formed using NV NT blocks may be used in memory arrays,such as the memory arrays described in U.S. patent application Ser. Nos.11/280,786 and 11/274,967. Also, NV NT switches formed using NV NTblocks may be used in non-volatile shadow latches to form register filesused in logic circuits, such as the register files described in U.S.patent application Ser. No. 11/280,599. These scalable NV NT Switchesformed using NV NT blocks may be used instead of stacked capacitors inDRAM cells to create a less complex scalable nonvolatile storagestructure.

Methods of Fabrication of NV NT Switches Using Nonvolatile NanotubeBlocks

Some embodiments of methods of depositing and patterning a CNT layer, orlayers, of carbon nanotubes (CNTs) from CNT dispersion in aqueous ornon-aqueous solutions that may be used to fabricate nonvolatilenantotube blocks are described in incorporated patent references.Examples of such NV NT blocks are illustrated in 3-D representations inFIGS. 56D, 56E, 56F, 57A and 57A′. Such methods may be used to fabricatenonvolatile nanotube switches using NV NT blocks as described furtherabove with respect to FIGS. 58A-65. Such methods may also be used tofabricate 3-D memory cells using NV NT blocks such as illustrated bycross section 4000 in FIG. 40, where nanotube element 4050 is a NV NTblock with top and bottom contacts, and by cross section 4785illustrated in FIG. 47 where nanotube elements 4740-1 and 4740-2 are NVNT blocks with end contacts.

Some embodiments of methods of NV NT block fabrication may be extendedto include deposition of a CNT layer, or layers, from CNT dispersions ina sacrificial polymer dissolved in an organic solvent as described withrespect to methods 6600A of fabrication illustrated in FIG. 66A. Suchmethods may, in some embodiments, be used to enhance electricalperformance such as cyclability (number of ON/OFF cycles) and/orfacilitate NV NT block fabrication to enable, for example, NV NT blockswith more closely spaced top and bottom contact locations as illustratedby comparing NV NT block 5730 shown in a 3-D representation in FIG. 57Bwith NV NT block 5710 shown in a 3-D representation in FIG. 57A. ShorterNV NT switch channel length L_(SW-CH), corresponding to top-to-bottomcontact separation may reduce NV NT switch operating voltage asdescribed further above with respect to FIG. 10. The sacrificial polymermay remain in the NV NT structure 5730 shown in a 3-D representation inFIG. 57B, or may be removed from the NV NT block by evaporation,typically at temperatures in the range of 200 deg C. to 400 deg C., asillustrated by NV NT block 5730′ shown in a 3-D representation in FIG.57B′.

Some embodiments of methods of NV NT block fabrication may also beextended to include the addition of performance enhancing material suchas a porous dielectric, for example, as described with respect tomethods 6600B of fabrication illustrated in FIG. 66B and methods 6600Cof fabrication illustrated in FIG. 66C. Block 5750 shown in a 3-Drepresentation in FIG. 57C illustrates a NV NT block that incorporatesperformance enhancing material such as a porous dielectric.

Methods of Fabrication of Nonvolatile Nanotube Blocks Using aSacrificial Polymer

FIG. 66A illustrates certain methods 6600A of fabrication of enhanced NVNT blocks. In general, methods 6605 fabricate support circuits andinterconnections in and out of a semiconductor substrate separately,e.g., with methods 2710 described further above with respect to FIGS.27A-27B. Exemplary methods 6605 deposit and pattern semiconducting,metallic, and insulating layers and form structures prior to CNT layerdeposition.

Next, methods 6608 deposit a CNT layer, or layers, from CNT dispersionsin a sacrificial polymer dissolved in an organic solvent. For example,sacrificial polymer polypropylene carbonate (PPC) dissolved in one ormore organic solvents such as NMP or cyclohexanone available in theindustry. A description of the properties of polypropylene carbonate maybe found, for example, in referenced technical data available from thecompany Empower Materials, Inc. While sacrificial polymer PPC is used inthis example, other sacrificial polymers such as Unity sacrificialpolymer and polyethylene carbonate sacrificial polymer may also be used.At this point in the process, the CNT layer may be patterned continuingwith fab. flow 1A illustrated in FIG. 66A. Alternatively, additionallayers may be added to be followed by patterning of multiple layersincluding the CNT layer continuing with fab. flow 2A illustrated in FIG.66A. Exemplary methods will be described first with respect to CNT layerpatterning (fab. flow 1A), and then followed by methods of patterningmultiple layers including the CNT layer (fab. flow 2A).

Continuing methods 6600A of fabrication description using fab. flow 1A,next, methods 6610 then pattern (etch) the CNT layer using nanotubeetching techniques described in incorporated patent references. Incertain embodiments, the methods include substantially removing (e.g.,etching) the sacrificial polymer such as polypropylene carbonate (PPC)in exposed regions. This removal may be performed, e.g., usinganisotropic physical etch, etch as Ar ion milling; or reactive ionetching (RIE) involving O₂ plasma; or a combination of both.

Next, methods 6612 complete NV NT block fabrication. Such methodsinclude deposition and patterning a conductor layer to form terminals incontact with the NV NT block at a top, side, or end region, orcombinations of contacts thereof as illustrated in FIGS. 58A-58D, forexample. Alternatively, such methods may include depositing andpatterning an insulating layer and then a conductor layer as illustratedin FIG. 60A-60C.

At this point in the process, NV NT switches incorporating NV NT blockshave been formed, and methods 6680 complete the fabrication of chipsincluding passivation and package interconnect means using knownindustry methods of fabrication. The encapsulated NV NT blocks include asacrificial polymer as illustrated with respect to block 5730 shown in a3-D representation in FIG. 57B.

Alternatively, methods 6615 may substantially remove, (e.g., evaporate)the sacrificial polymer such as polypropylene carbonate for example, byheating the wafer to a temperature in the range of 200 deg. C. to 400deg. C. In this example, NV NT block 5730 becomes like NV NT block 5730′shown in a 3-D representation in FIG. 57B′ with NV NT blocks havingsubstantially only CNT fabric formed of individual nanotubes.

Then, methods 6680 complete the fabrication of chips includingpassivation and package interconnect means using known industry methodsof fabrication. The encapsulated NV NT blocks substantially do notinclude a sacrificial polymer as illustrated with respect to block 5730′shown in a 3-D representation in FIG. 57B′. At this point in theprocess, method 6600A of fabrication using fab. flow 1A ends.

In an alternative fabrication sequence, methods 6600A of fabricationthat include fab. flow 2A use methods 6620 to deposit additionalfabrication layers added to the CNT layer, or layers, deposited in aprevious step using methods 6608 of fabrication.

Next, methods 6622 pattern multiple layers including the CNT layer.Known industry methods remove (etch) exposed regions of metal,insulator, and semiconductor layers. Exemplary methods of CNT layer etchare described in incorporated patent references. Some methods remove(etch) sacrificial polymer such as polypropylene carbonate (PPC) inexposed regions. Exemplary methods may include anisotropic physicaletch, etch as Ar ion milling; or reactive ion etching (RIE) involving O₂plasma; or a combination of both.

By way of example, NV NT switch 6400/6400′ illustrated in FIGS. 64A-64Cshows the formation of NV NT block 6410 using a top contact (andterminal) conductor and an insulating layer as a mask to remove (etch)the underlying CNT layer. Cross section 4000 illustrated in FIG. 40 alsoshows the formation of the NV NT block referred to as nanotube element4050 by patterning additional layers above the NV NT block surface.However, substantial removal of exposed regions of a sacrificial polymeris not illustrated in these two examples.

At this point in the process, NV NT switches incorporating NV NT blockshave been formed, and methods 6680 complete the fabrication of chipsincluding passivation and package interconnect means using knownindustry methods of fabrication. The encapsulated NV NT blocks include asacrificial polymer as illustrated with respect to block 5730 shown in a3-D representation in FIG. 57B.

Alternatively, methods 6615 substantially remove, (e.g., evaporate) thesacrificial polymer such as polypropylene carbonate for example, byheating the wafer to a temperature in the range of 200 deg. C. to 400deg. C. In this example, NV NT block 5730 becomes like NV NT block 5730′shown in a 3-D representation in FIG. 57B′ with NV NT blocks havingsubstantially only CNT fabric formed of individual nanotubes.

Then, methods 6680 complete the fabrication of chips includingpassivation and package interconnect means using known industry methodsof fabrication. The encapsulated NV NT blocks substantially do notinclude a sacrificial polymer as illustrated with respect to block 5730′shown in a 3-D representation in FIG. 57B′. At this point in theprocess, method 6600A of fabrication using fab. flow 2A ends.

A First Method of Fabrication of Nonvolatile Nanotube Blocks Having aPorous Dielectric

FIG. 66B illustrates methods 6600B of fabrication of enhanced NV NTblocks. In general, methods 6605 fabricate support circuits andinterconnections in and out of a semiconductor substrate, e.g., usingmethods 2710 described further above with respect to FIG. 27. Methods6605 deposit and pattern semiconducting, metallic, and insulating layersand form structures prior to CNT layer deposition.

Next, methods 6608 deposit a CNT layer, or layers, from CNT dispersionsin a sacrificial polymer dissolved in an organic solvent. For example,sacrificial polymer polypropylene carbonate (PPC) dissolved in anorganic solvent such as NMP or cyclohexanone available in the industry.At this point in the process, methods 6600B of fabrication process flowmay proceed with fab. flow 1B. Alternatively, methods 6600B offabrication process flow may proceed with fab. flow 2B. Exemplarymethods 6600B of fabrication will be described first with respect tofab. flow 1B, and then followed by methods 6600B of fabrication withrespect to fab. flow 2A.

Continuing methods 6600B of fabrication description using fab. flow 1B,next, methods 6625 then pattern (etch) the CNT layer using nanotubeetching techniques described in incorporated patent references. In someembodiments, methods substantially remove (e.g., etch) the sacrificialpolymer such as polypropylene carbonate (PPC) in exposed regions.Exemplary methods include anisotropic physical etch, etch as Ar ionmilling; or reactive ion etching (RIE) involving O₂ plasma; or acombination of both.

Next, methods 6628 substantially remove (e.g., evaporate) thesacrificial polymer such as polypropylene carbonate for example, byheating the wafer to a temperature in the range of 200 deg. C. to 400deg. C. In this example, NV NT block 5730 becomes like NV NT block 5730′shown in a 3-D representation in FIG. 57B′ with NV NT blocks havingsubstantially only CNT fabric formed of individual nanotubes.

Next, methods 6630 form a performance enhancing material such as aporous dielectric. Porous dielectric may be formed using spin-on glass(SOG) and spin-on low-K organic dielectrics as described in a paper byS. Thanawala et al., “Reduction in the Efffective Dielectric Constant ofIntegrated Interconnect Structures Through an All-Spin-On Strategy”,available from Honeywell Electronic Materials, Honeywell InternationalInc., Sunnyvale, Calif. 94089. Alternatively, individual nanotubesforming nonvolatile nanotube block structures may be derivitizedcovalently or non-covalently to generate a modified surface as describedin USPTO Patent Pub. No. 2006/0193093 which includes common inventorBertin and is hereby incorporated by reference in its entirety.Derivitized individual nanotubes may include oxygen, fluorine, chlorine,bromine, iodine (or other) atoms, for example, thereby formingnonvolatile nanotube blocks that include a porous dielectric forperformance enhancement purposes.

Next, methods 6632 complete NV NT block fabrication. Such methodsinclude deposition and patterning a conductor layer to form terminals incontact with the NV NT block at a top, side, or end region, orcombinations of contacts thereof. In this example, encapsulated NV NTblocks with top and bottom contacts include a performance enhancingmaterial such as a porous dielectric as illustrated with respect toblock 5750 shown in a 3-D representation in FIG. 57C.

At this point in the process, NV NT switches incorporating NV NT blockshave been formed, and methods 6680 complete the fabrication of chipsincluding passivation and package interconnect means using knownindustry methods of fabrication. The encapsulated NV NT blocks include aperformance enhancing material such as a porous dielectric asillustrated with respect to block 5750 shown in a 3-D representation inFIG. 57C.

In an alternative fabrication sequence, methods 6600B of fabricationthat include fab. flow 2B use methods 6635 to substantially remove(e.g., evaporate) the sacrificial polymer such as polypropylenecarbonate from the CNT layer for example, by heating the wafer to atemperature in the range of 200 deg. C. to 400 deg. C.

Next, methods 6638 form a performance enhancing material such as aporous dielectric. Porous dielectric may be formed using spin-on glass(SOG) and spin-on low-K organic dielectrics as described in a paper byS. Thanawala et al., “Reduction in the Efffective Dielectric Constant ofIntegrated Interconnect Structures Through an All-Spin-On Strategy”,available from Honeywell Electronic Materials, Honeywell InternationalInc., Sunnyvale, Calif. 94089. Alternatively, individual nanotubesforming nonvolatile nanotube block structures may be derivitizedcovalently or non-covalently to generate a modified surface as describedin USPTO Patent Pub. No. 2006/0193093. Derivitized individual nanotubesmay include oxygen, fluorine, chlorine, bromine, iodine (or other)atoms, for example, thereby forming nonvolatile nanotube blocks thatinclude a porous dielectric for performance enhancement purposes.

Next, methods 6640 of fabrication deposit additional fabrication layersadded to the CNT layer, or layers, such as conductor, insulating, orsemiconducting layers deposited using industry methods of fabrication.

Next, methods 6642 pattern multiple layers including the CNT layer.Known industry methods remove (etch) exposed regions of metal,insulator, and semiconductor layers. Exemplary methods of CNT layer etchare described in incorporated patent references. Exemplary methodsremove (etch) exposed portions of the performance enhancing materialsuch as a porous dielectric using known industry methods for etchingdielectric material.

At this point in the process, NV NT switches incorporating NV NT blockshave been formed, and methods 6680 complete the fabrication of chipsincluding passivation and package interconnect means using knownindustry methods of fabrication. The encapsulated NV NT blocks include aperformance enhancing material such as a porous dielectric asillustrated with respect to block 5750 shown in a 3-D representation inFIG. 57C.

A Second Method of Fabrication of Nonvolatile Nanotube Blocks Having aPorous Dielectric

FIG. 66C illustrates methods 6600C of fabrication of enhanced NV NTblocks. In general, methods 6605 fabricate support circuits andinterconnections in and out of a semiconductor substrate, e.g., usingmethods 2710 described further above with respect to FIG. 27. In someembodiments, methods 6605 deposit and pattern semiconducting, metallic,and insulating layers and form structures prior to CNT layer deposition.

Next, methods 6650 deposit a CNT layer, or layers, from CNT dispersionin aqueous or non-aqueous solutions are used to fabricate nonvolatilenanotube blocks as described in incorporated patent references. At thispoint in the process, methods 6600C of fabrication process flow mayproceed with fab. flow 1C. Alternatively, methods 6600C of fabricationprocess flow may proceed with fab. flow 2C. Exemplary methods 6600C offabrication will be described first with respect to fab. flow 1C, andthen followed by methods 6600C of fabrication with respect to fab. flow2C.

Continuing methods 6600C of fabrication description using fab. flow 1C,next, methods 6655 then pattern (etch) the CNT layer using nanotubeetching techniques described in incorporated patent references.

Next, methods 6658 form a performance enhancing material such as aporous dielectric. Porous dielectric may be formed using spin-on glass(SOG) and spin-on low-K organic dielectrics as described in a paper byS. Thanawala et al., “Reduction in the Efffective Dielectric Constant ofIntegrated Interconnect Structures Through an All-Spin-On Strategy”,available from Honeywell Electronic Materials, Honeywell InternationalInc., Sunnyvale, Calif. 94089. Alternatively, individual nanotubesforming nonvolatile nanotube block structures may be derivitizedcovalently or non-covalently to generate a modified surface as describedin USPTO Patent Pub. No. 2006/0193093. Derivitized individual nanotubesmay include oxygen, fluorine, chlorine, bromine, iodine (or other)atoms, for example, thereby forming nonvolatile nanotube blocks thatinclude a porous dielectric for performance enhancement purposes.

Next, methods 6660 complete NV NT block fabrication. Such methodsinclude deposition and patterning a conductor layer to form terminals incontact with the NV NT block at a top, side, or end region, orcombinations of contacts thereof. In this example, encapsulated NV NTblocks with top and bottom contacts include a performance enhancingmaterial such as a porous dielectric as illustrated with respect toblock 5750 shown in a 3-D representation in FIG. 57C.

At this point in the process, NV NT switches incorporating NV NT blockshave been formed, and methods 6680 complete the fabrication of chipsincluding passivation and package interconnect means using knownindustry methods of fabrication. The encapsulated NV NT blocks include aperformance enhancing material such as a porous dielectric asillustrated with respect to block 5750 shown in a 3-D representation inFIG. 57C.

In an alternative fabrication sequence, methods 6600C of fabricationthat include fab. flow 2C uses methods 6665 to form a performanceenhancing material such as a porous dielectric. Porous dielectric may beformed using spin-on glass (SOG) and spin-on low-K organic dielectricsas described in a paper by S. Thanawala et al., “Reduction in theEfffective Dielectric Constant of Integrated Interconnect StructuresThrough an All-Spin-On Strategy”, available from Honeywell ElectronicMaterials, Honeywell International Inc., Sunnyvale, Calif. 94089.Alternatively, individual nanotubes forming nonvolatile nanotube blockstructures may be derivitized covalently or non-covalently or mixed withpristine nanotubes to generate a modified surface as described in USPTOPatent Pub. No. 2006/0193093. Derivitized individual nanotubes mayinclude oxygen, fluorine, chlorine, bromine, iodine (or other) atoms,for example, thereby forming nonvolatile nanotube blocks that include aporous dielectric for performance enhancement purposes.

Next, methods 6670 of fabrication deposit additional fabrication layersadded to the CNT layer, or layers, such as conductor, insulating, orsemiconducting layers deposited using methods industry methods offabrication.

Next, methods 6675 pattern multiple layers including the CNT layer.Known industry methods substantially remove (etch) exposed regions ofmetal, insulator, and semiconductor layers. Exemplary methods of CNTlayer etch are described in incorporated patent references. In someembodiments, methods remove (etch) exposed portions of the performanceenhancing material such as a porous dielectric by using known industrymethods for etching dielectric material, especially oxygen plasma andreactive ion etching with gasses that are capable of removing carbonnanotubes which are unprotected by photoresist or other processingmaterials. Such etches may be isotropic or anisotropic depending uponthe orientation required.

At this point in the process, NV NT switches incorporating NV NT blockshave been formed, and methods 6680 complete the fabrication of chipsincluding passivation and package interconnect means using knownindustry methods of fabrication. The encapsulated NV NT blocks include aperformance enhancing material such as a porous dielectric asillustrated with respect to block 5750 shown in a 3-D representation inFIG. 57C.

3-Dimensional Cell Structure of Nonvolatile Cells Using NV NT DevicesHaving Vertically Oriented Diodes and Nonvolatile Nanotube Blocks asNonvolatile NT Switches Using Top and Bottom Contacts to FormCathode-on-NT Switches

FIG. 67 illustrates cross section 6700 including cells C00 and C01 in a3-D memory embodiment. Nanotube layers are deposited by coating,spraying, or other means on a planar contact surface on previouslydefined diode-forming layers as illustrated in FIG. 40 shown furtherabove. Cross section 6700 illustrated in FIG. 67 corresponds tostructure 4000 illustrated in FIG. 40, with some additional detailassociated with an cathode-on-NT implementation and element numbers tofacilitate description of methods of fabrication. Trench etching afterthe deposition of insulator, semiconductor, conductor, and nanotubelayers form sidewall boundaries that define nonvolatile nanotubeblock-based nonvolatile nanotube diode 3-D memory cells and definenonvolatile nanotube block dimensions, diode dimensions, and thedimensions of all other structures in the three dimensional nonvolatilestorage cells. The horizontal 3-D cell dimensions (X and Y approximatelyorthogonal directions) of all cell structures are formed by trenchetching and are therefore self-aligned as fabricated. The verticaldimension (Z) is determined by the thickness and number of verticallayers used to form the 3-D cell. FIG. 67 illustrates cross section 6700along a word line (X) direction. Stacked series-connectedvertically-oriented steering diodes and nonvolatile nanotube blockswitches are symmetrical and have approximately the same cross sectionaldimensions in both X and Y directions. Cross section 6700 illustratesarray cells in which the steering diode is connected to the bottom(lower level) contact of the nonvolatile nanotube block in acathode-on-NT configuration. Word lines are oriented along the X axisand bit lines along the Y axis as illustrated in perspective in FIG.33A.

Some embodiments of methods 2710 described further above with respect toFIG. 27A are used to define support circuits and interconnections 6701.

Next, methods 2730 illustrated in FIG. 27B deposit and planarizeinsulator 6703. Interconnect means through planar insulator 6703 (notshown in cross section 6700 but shown above with respect to crosssection 2800″ in FIG. 28C) may be used to connect metal array lines in3-D arrays to corresponding support circuits and interconnections 6701.By way of example, bit line drivers in BL driver and sense circuits 2640may be connected to bit lines BL0 and BL1 in array 2610 of memory 2600illustrated in FIG. 26A described further above, and in cross section6700 illustrated in FIG. 67. At this point in the fabrication process,methods 2740 may be used to form a memory array on the surface ofinsulator 6703, interconnected with memory array support structure 6705illustrated in FIG. 67. Memory array support structure 6705 correspondsto memory array support structure 3405 illustrated in FIG. 47, andsupport circuits & interconnections 6701 correspond to support circuits& interconnections 3401, and insulator 6703 corresponds to insulator3403 except for some changes to accommodate a new memory array structurefor 3-D memory cells that include nonvolatile nanotube blocks with top(upper level) and bottom (lower level) contacts.

Exemplary methods 2740 illustrated in FIG. 27B deposit and planarizemetal, polysilicon, insulator, and nanotube element layers to formnonvolatile nanotube diodes which, in this example, include multiplevertically oriented diode and nonvolatile nanotube block (NV NT block)switch cathode-on-NT series pairs. Individual cell boundaries are formedin a single etch step for the X direction (and a separate single etchfor the Y direction), each cell having a single NV NT Diode defined by asingle trench etch step after layers, except the WL0 layer, have beendeposited and planarized, in order to eliminate accumulation ofindividual layer alignment tolerances that would substantially increasecell area. Individual cell dimensions in the X direction are F (1minimum feature) as illustrated in FIG. 40 and corresponding FIG. 67,and also F in the Y direction (not shown) which is approximatelyorthogonal to the X direction, with a periodicity in X and Y directionsof 2F. Hence, each cell occupies an area of approximately 4F².

NV NT blocks with top (upper level) and bottom (lower level) contacts,illustrated further above in FIG. 40 and corresponding FIG. 67 bynanotube elements 4050-1 and 4050-2, are further illustrated inperspective drawings in FIGS. 57A-57C further above. NV NT block devicestructures and electrical ON/OFF switching results are described withrespect to FIGS. 64A-64C and 65 further above. Methods of fabrication ofNV NT blocks with top and bottom contacts are described with respect tomethods 6600A, 6600B, and 6600C illustrated in FIGS. 66A, 66B, and 66C,respectively. NV NT blocks with top and bottom contacts have channellengths L_(SW-CH) approximately equal to the separation between top andbottom contacts, 35 nm for example. A NV NT block switch cross section Xby Y may be formed with X=Y=F, where F is a minimum technology nodedimension. For a 35 nm technology node, a NV NT block may havedimensions of 35×35×35 nm; for a 22 nm technology node, a NV NT blockmay have dimensions of 22×22×35 nm, for example.

Methods fill trenches with an insulator; and then methods planarize thesurface. Then, methods deposit and pattern word lines on the planarizedsurface.

The fabrication of vertically-oriented 3D cells illustrated in FIG. 67proceeds as follows. In some embodiments, methods deposit a bit linewiring layer on the surface of insulator 6703 having a thickness of 50to 500 nm, for example, as described further below with respect to FIGS.68A-68I. Fabrication of the vertically-oriented diode portion ofstructure 6700 may be the same as in FIGS. 34A and 34B described furtherabove and are incorporated in methods of fabrication described withrespect to FIGS. 68A-68I. Methods etch the bit line wiring layer anddefine individual bit lines such as bit line conductors 6710-1 (BL0) and6710-2 (BL1). Bit lines such as BL0 and BL1 are used as array wiringconductors and may also be used as anode terminals of Schottky diodes.Alternatively, more optimum Schottky diode junctions may be formed usingmetal or silicide contacts (not shown) in contact with N polysiliconregions 6720-1 and 6720-2, while also forming ohmic contacts with bitline conductors 6710-1 and 6710-2. N polysilicon regions 6720-1 and6720-2 may be doped with arsenic or phosphorus in the range of 10¹⁴ to10¹⁷ dopant atoms/cm³ for example, and may have a thickness range of 20nm to 400 nm, for example.

FIG. 67 illustrates a cathode-to-NT type NV NT diodes formed withSchottky diodes. However, PN or PIN diodes may be used instead ofSchottky diodes as described further below with respect to FIG. 68A.

The electrical characteristics of Schottky (and PN, PIN) diodes may beimproved (low leakage, for example) by controlling the materialproperties of polysilicon, for example polysilicon deposited andpatterned to form polysilicon regions 6820-1 and 6820-2. Polysiliconregions may have relatively large or relatively small grain boundarysizes that are determined by methods of fabrication such as anneal timesand temperatures for example. In some embodiments, SOI depositionmethods in the semiconductor industry may be used that result inpolysilicon regions that are single crystalline (no longer polysilicon),or nearly single crystalline, for further electrical propertyenhancement such as low diode leakage currents.

Examples of contact and conductors materials include elemental metalssuch as Al, Au, Pt, W, Ta, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb,Sn, as well as metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW,other suitable conductors, or conductive nitrides such as TiN, oxides,or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x). In somecases conductors such as Al, Au, W, Cu, Mo, Ti, and others may be usedas both contact and conductors materials as well as anodes for Schottkydiodes. However, in other cases, optimizing anode material for lowerforward voltage drop and lower diode leakage is advantageous. Schottkydiode anode materials may be added (not shown) between conductors 6710-1and 6710-2 and polysilicon regions 6720-1 and 6720-2, respectively. Suchanode materials may include Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo,Na, Ni, Os, Pb, Pd, Pt, Rb, Ru, Ti, W, Ta, Zn and other elementalmetals. Also, silicides such as CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂,WSi₂, and ZrSi₂ may be used. Schottky diodes formed using such metalsand silicides are illustrated in the reference by NG, K. K. “CompleteGuide to Semiconductor Devices”, Second Edition, John Wiley & Sons,2002, pp. 31-41, the entire contents of which are incorporated herein byreference.

Next, having completed Schottky diode select devices, methods form N+polysilicon regions 6725-1 and 6725-2 to contact N polysilicon regions6720-1 and 6720-2, respectively. N+ polysilicon is typically doped witharsenic or phosphorous to 10²⁰ dopant atoms/cm³, for example, and has athickness of 20 to 400 nm, for example. N and N+ polysilicon regiondimensions are defined by trench etching near the end of the processflow.

Next, methods form bottom (lower level) contact regions 4030-1 and4030-2 with ohmic or near ohmic contacts to polysilicon regions 6725-1and 6725-2, respectively. Examples of contact and conductors materialsinclude elemental metals such as Al, Au, W, Ta, Cu, Mo, Pd, Ni, Ru, Ti,Cr, Ag, In, Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu,TiPd, PbIn, and TiW, other suitable conductors, or conductive nitridessuch as TiN, oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x)and TiSi_(x).

Next, methods form NV NT block 4050-1 and 4050-2 on the surface ofcontact regions 4030-1 and 4030-2, respectively, having the nanotubeelement length of the NV NT blocks defined by the nanotube thickness inthe vertical Z direction and X-Y cross section defined by trench etchingnear the end of the process flow. Note that NV NT block 4050-1 in FIG.67 corresponds to nanotube element 4050 in FIG. 40. In order to enhancethe density of cells C00 and C01, NV NT blocks 4050-1 and 4050-2illustrated in FIG. 67 include simple top and bottom contacts withintrench-defined cell boundaries.

Next, methods form top (upper level) contacts 4065-1 and 4065-2 on thetop surfaces of NV NT blocks 4050-1 and 4050-2, respectively, with X andY dimensions defined by trench etching near the end of the process flow.

Next, methods form (etch) trench openings 4075, 4075A, and 4075B, eachof width F, thereby forming inner and outer sidewalls of cells C00 andC01 and corresponding top (upper level) and bottom (lower level)contacts, nanotube elements, and insulators. Bottom (lower level)contacts 4030-1 and 4030-2 form an electrical connection between NV NTblocks 4050-1 and 4050-2, respectively, and corresponding underlyingsteering diode cathode terminals, and form bit lines 6710-1 and 6710-2.Trench formation (etching) stops at the surface of insulator 6703.

Next, methods fill trench openings 4075, 4075A, and 4075B with aninsulator 4060, 4060A, and 4060B, respectively, such as TEOS andplanarize the surface. All trenches can be formed simultaneously.

Next, methods deposit and planarize a word line layer.

Next, methods pattern word line 6770.

Next, methods 2750 illustrated in FIG. 27A complete fabrication ofsemiconductor chips with nonvolatile memory arrays using nonvolatilenanotube diode cell structures including passivation and packageinterconnect means using known industry methods.

Nonvolatile nanotube diodes forming cells C00 and C01 correspond tononvolatile nanotube diode 1200 schematic in FIG. 12, also illustratedschematically by NV NT diode 6780 in FIG. 67, one in each of cells C00and C01. Cells C00 and C01 illustrated in cross section 6700 in FIG. 67correspond to corresponding cells C00 and C01 shown schematically inmemory array 2610 in FIG. 26A, and bit lines BL0 and BL1 and word lineWL0 correspond to array lines illustrated schematically in memory array2610.

Embodiments of methods 2700 illustrated in FIGS. 27A and 27B may be usedto fabricate nonvolatile memories using NV NT diode devices withcathode-to-NT switch connections to NV NT block switches such as thoseshown in cross section 6700 illustrated in FIG. 67 and as describedfurther below with respect to FIGS. 68A-68I. Structures such as crosssection 6700 may be used to fabricate memory 2600 illustratedschematically in FIG. 26A.

Methods of Fabricating 3-Dimensional Cell Structure of Nonvolatile CellsUsing NV NT Devices Having Vertically Oriented Diodes and NonvolatileNanotube Blocks as Nonvolatile NT Switches Using Top and Bottom Contactsto Form Cathode-on-NT Switches

Embodiments of methods 2710 illustrated in FIG. 27A may be used todefine support circuits and interconnects similar to those describedwith respect to memory 2600 illustrated in FIG. 26A as described furtherabove. Methods 2710 apply known semiconductor industry techniques designand fabrication techniques to fabricated support circuits andinterconnections 6801 in and on a semiconductor substrate as illustratedin FIG. 68A. Support circuits and interconnections 6801 include FETdevices in a semiconductor substrate and interconnections such as viasand wiring above a semiconductor substrate. FIG. 68A corresponds to FIG.34A illustrating a Schottky diode structure, except that an optionalconductive Schottky anode contact layer 3415 shown in FIG. 34A is notshown in FIG. 68A. Note that FIG. 34A′ may be used instead of FIG. 34A′as a starting point if a PN diode structure is desired. If N polysiliconlayer 3417 in FIG. 34A′ were replaced with an intrinsically dopedpolysilicon layer instead (not shown), then a PIN diode would be formedinstead of a PN diode. Therefore, while the structure illustrated inFIG. 68A illustrates a Schottky diode structure, the structure may alsobe fabricated using either a PN diode or a PIN diode.

Methods of fabrication for elements and structures for support circuits& interconnections 6801, insulator 6803, memory array support structure6805, conductor layer 6810, N polysilicon layer 6820, N+ polysiliconlayer 6825, and bottom (lower level) contact layer 6830 illustrated inFIG. 68A are described further above with respect to FIGS. 34A and 34B,where support circuits & interconnections 6801 correspond to supportcircuits & interconnections 3401; insulator 6803 corresponds toinsulator 3403; memory array support structure 6805 corresponds tomemory array support structure 3405; conductor layer 6810 corresponds toconductor layer 3410; N polysilicon layer 6820 corresponds to Npolysilicon layer 3420; N+ polysilicon layer 6825 corresponds to N+polysilicon layer 3425; and bottom (lower level) contact layer 6830corresponds to bottom (lower level) contact layer 3430.

Next, methods deposit a nanotube layer 6835 on the planar surface ofcontact layer 6830 as illustrated in FIG. 68B using spin-on of multiplelayers, spray-on, or other means. Nanotube layer 6835 may be in therange of 10-200 nm for example. Exemplary devices of 35 nm thicknesseshave been fabricated and switched between ON/OFF states as illustratedin FIGS. 64A-64C and 65. Methods of fabrication of NV NT blocks with topand bottom contacts are described with respect to methods 6600A, 6600B,and 6600C illustrated in FIGS. 66A, 66B, and 66C, respectively.

At this point in the fabrication process, methods deposit top (upperlevel) contact layer 6840 on the surface of nanotube layer 6835 asillustrated in FIG. 68B. Top (upper level) contact layer 6840 may be 10to 500 nm in thickness, for example. Top (upper level) contact layer6840 may be formed using Al, Au, Ta, W, Cu, Mo, Pd, Pt, Ni, Ru, Ti, Cr,Ag, In, Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu, TiPd,PbIn, and TiW, other suitable conductors, or conductive nitrides such asTiN, oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) andTiSi_(x), for example.

Next methods deposit and pattern a masking layer 6850 on top (upperlevel) contact layer 6840 as illustrated in FIG. 68C using knownindustry methods. Masking layer 6850 may be in the range of 10 to 500 nmthick and be formed using resist such as photoresist, e-beam resist, orconductor, semiconductor, or insulator materials. Mask layer 6850openings 6855, 6855A and 6855B expose underlying regions for purposes oftrench etching. The mask opening may be aligned to alignment marks inplanar insulating layer 6803 for example; the alignment is not critical.In order to achieve minimum cell dimensions, mask layer 6850 openings6855, 6855A, and 6855B are approximately equal to the minimum allowedtechnology dimension F. F may be 90 nm, 65 nm, 45 nm, 35 nm, 25 nm, 12nm, or sub-10 nm, for example.

At this point in the process, mask layer 6850 openings 6855, 6855A, and6855B may be used for directional etching of trenches using methods thatdefine a cell boundary along the X direction for 3D cells using one NVNT diode with an internal cathode-to-nanotube connection per cell. U.S.Pat. No. 5,670,803, the entire contents of which are incorporated hereinby reference, to co-inventor Bertin, discloses a 3-D array (in thisexample, 3D-SRAM) structure with simultaneously trench-defined sidewalldimensions. This structure includes vertical sidewalls simultaneouslydefined by trenches cutting through multiple layers of doped silicon andinsulated regions in order avoid multiple alignment steps. Such trenchdirectional selective etch methods may cut through multiple conductor,semiconductor, oxide, and nanotube layers as described further abovewith respect to trench formation in FIGS. 34A-34FF and 36A-36FF. In thisexample, selective directional trench etch (RIE) removes exposed areasof top (upper level) contact layer 6840 to form upper level contactregions 6840-1 and 6840-2; removes exposed areas of nanotube layer 6835to form nanotube regions 6835-1 and 6835-2; removes exposed areas ofbottom (lower level) contact layer 6830 to form bottom (lower level)contact regions 6830-1 and 6830-2; directional etch removes exposedareas of N+ polysilicon layer 6825 to form N+ polysilicon regions 6825-1and 6825-2; removes exposed areas of polysilicon layer 6820 to form Npolysilicon regions 6820-1 and 6820-2; and removes exposed areas ofconductor layer 6810 to form conductor regions 6810-1 and 6810-2,stopping at the surface of insulator 6803 and simultaneously formingtrench openings 6860, 6860A, and 6860B as illustrated in FIG. 68D.

Next methods fill trench openings 6860, 6860A, and 6860B with insulators6865, 6865A, and 6865B, respectively, such as TEOS for example andplanarize as illustrated in FIG. 68E.

Next, methods deposit and planarize a conductor layer 6870 that contactstop (upper level) contacts 6840-1 and 6840-2 as illustrated in FIG. 68F.

Next, conductor layer 6870 is patterned to form word lines approximatelyorthogonal to conductors (bit lines) 6810-1 and 6810-2 as illustratedfurther below.

At this point in the process, cross section 6875 illustrated in FIG. 68Fhas been fabricated, and includes NV NT diode cell dimensions of F(where F is a minimum feature size) and cell periodicity 2F defined inthe X direction as well as corresponding array bit lines. Next, celldimensions used to define dimensions in the Y direction are formed bydirectional trench etch processes similar to those described furtherabove with respect to cross section 6875 illustrated in FIG. 68F.Trenches used to define dimensions in the Y direction are approximatelyorthogonal to trenches used to define dimensions in the X direction.Cross sections of structures in the Y (bit line) direction areillustrated with respect to cross section Y-Y′ illustrated in FIG. 68F.

Next, methods deposit and pattern a masking layer such as masking layer6880 with openings 6882, 6882A, and 6882B on the surface of word linelayer 6870 as illustrated in FIG. 68G. Masking layer 6880 openings maybe non-critically aligned to alignment marks in planar insulator 6803.Openings 6882, 6882A, and 6882B in mask layer 6880 determine thelocation of trench directional etch regions, in this case trenches areapproximately orthogonal to bit lines such as bit line 6810-1 (BL0).

At this point in the process, openings 6882, 6882A, and 6882B in maskinglayer 6880 may be used for directional etching of trenches using methodsthat define new cell boundaries along the Y direction for 3D cells usingone NV NT diode with an internal cathode-to-nanotube connection percell. All trenches and corresponding cell boundaries may be formedsimultaneously (e.g., using one etch step) using the methods offabrication as used to form X-direction trenches as described withrespect to FIG. 68D. This structure includes vertical sidewallssimultaneously defined by trenches; X and Y direction dimensions andmaterials are the same. In this example, methods of selectivedirectional trench etch (RIE) removes exposed areas of conductor layer6870 to form word lines 6870-1 (WL0) and 6870-2 (WL1) approximatelyorthogonal to bit lines 6810-1 (BL0) and 6810-2 (BL1); top (upper level)contact layer 6840-1 to form upper level contact regions 6840-1′ and6840-1″; removes exposed areas of nanotube layer 6835-1 to form nanotuberegions 6835-1′ and 6835-1″; removes exposed areas of bottom (lowerlevel) contact layer 6830-1 to form bottom (lower level) contact regions6830-1′ and 6830-1″; selective directional etch removes exposed areas ofN+ polysilicon layer 6825-1 to form N+ polysilicon regions 6825-1′ and6825-1″; removes exposed areas of polysilicon layer 6820-1 to form Npolysilicon regions 6820-1′ and 6820-1″; and stops etching at thesurface of exposed areas of conductor layer 6810-1 as illustrated inFIG. 68H.

Next methods fill trench openings 6884, 6884A, and 6884B with insulators6885, 6885A, and 6885B such as TEOS for example and planarize asillustrated by cross section 6890 in FIG. 68I. At this point in theprocess, nonvolatile nanotube diode-based cells are completely formedand interconnected with bit lines and approximately orthogonal wordlines. Cross section 6875 illustrated in FIG. 68F and cross section 6890illustrated in FIG. 68I are two cross sectional representation of thesame 3D nonvolatile memory array with cells formed with NV NT diodehaving vertically oriented steering (select) diodes and nonvolatilenanotube blocks. The cathode terminal of the diode contacts the lowerface of the block within the cell boundaries The anode side of the diodeis in contact with a bit line such as bit line 6810-1 (BL0) and the topface of the block is in contact with an approximately orthogonal wordline such as word line 6870-1 (WL0) as shown by cross section 6890 inFIG. 68I.

At this point in the process, cross sections 6875 and 6890 illustratedin FIGS. 68F and 68I, respectively, correspond to cross section 6700illustrated in FIG. 67 and have been fabricated with cells having avertically-oriented steering diodes and corresponding nonvolatilenanotube block switches in series, vertically-oriented (Z direction)channel lengths L_(SW-CH) are defined, including overall NV NT diodecell dimensions of 1F in the X direction and 1F in the Y direction, aswell as corresponding bit and word array lines. Cross section 6875 is across section of two adjacent cathode-to-nanotube type nonvolatilenanotube diode-based cells in the X direction and cross section 6890 isa cross section of two adjacent cathode-to-nanotube type nonvolatilenanotube diode-based cells in the Y direction. Cross sections 6875 and6890 include corresponding word line and bit line array lines. Thenonvolatile nanotube diodes form the steering and storage elements ineach cell illustrated in cross sections 6875 and 6890, and with eachcell having 1F by 1F dimensions. The spacing between adjacent cells is1F so the cell periodicity is 2F in both the X and Y directions.Therefore one bit occupies an area of 4F². At the 45 nm technology node,the cell area is less than 0.01 um², or approximately 0.002 um² in thisexample.

3-Dimensional Cell Structure of Nonvolatile Cells Using NV NT DevicesHaving Vertically Oriented Diodes and Nonvolatile Nanotube Blocks asNonvolatile NT Switches Using Top and Bottom Contacts to FormAnode-on-NT Switches

FIG. 69 illustrates cross section 6900 including cells C00 and C10 in a3-D memory embodiment. Nanotube layers are deposited by coating,spraying, or other means on a planar contact surface above previouslydefined diode-forming layers as illustrated in FIG. 40 shown furtherabove. Cross section 6900 illustrated in FIG. 69 correspond to structure4000 illustrated in FIG. 40, with some additional detail associated withan anode-on-NT implementation and element numbers to facilitatedescription of methods of fabrication. Trench etching after thedeposition of insulator, semiconductor, conductor, and nanotube layersform sidewall boundaries that define nonvolatile nanotube block-basednonvolatile nanotube diode 3-D memory cells and define nonvolatilenanotube block dimensions, diode dimensions, and the dimensions of allother structures in the three dimensional nonvolatile storage cells. Thehorizontal 3-D cell dimensions (X and Y approximately orthogonaldirections) of all cell structures are formed by trench etching and aretherefore self-aligned as fabricated. The vertical dimension (Z) isdetermined by the thickness and number of vertical layers used to formthe 3-D cell. FIG. 69 illustrates cross section 6900 along a bit line(Y) direction. Stacked series-connected vertically-oriented steeringdiodes and nonvolatile nanotube block switches are symmetrical and haveapproximately the same cross sections in both X and Y directions. Crosssection 6900 illustrates array cells in which the steering diode isconnected to the bottom (lower level) contact of the nonvolatilenanotube block in an anode-on-NT configuration. Word lines are orientedalong the X axis and bit lines along the Y axis as illustrated inperspective in FIG. 33A.

In some embodiments, methods 3010 described further above with respectto FIG. 30A are used to define support circuits and interconnections6901.

Next, methods 3030 illustrated in FIG. 30B deposit and planarizeinsulator 6903. Interconnect means through planar insulator 6903 (notshown in cross section 6900 but shown above with respect to crosssection 2800″ in FIG. 28C) may be used to connect metal array lines in3-D arrays to corresponding support circuits and interconnections 6901.By way of example, word line drivers in word line driver 2930 may beconnected to word lines WL0 and WL1 in array 2910 of memory 2900illustrated in FIG. 29A described further above, and in cross section6900 illustrated in FIG. 69. At this point in the fabrication process,methods 3040 may be used to form a memory array on the surface ofinsulator 6903, interconnected with memory array support structure 6905illustrated in FIG. 69. Memory array support structure 6905 correspondsto memory array support structure 3605 illustrated in FIG. 51, andsupport circuits & interconnections 6901 correspond to support circuits& interconnections 3601, and insulator 6903 corresponds to insulator3603 except for some changes to accommodate a new memory array structurefor 3-D memory cells that include nonvolatile nanotube blocks with top(upper level) and bottom (lower level) contacts.

In some embodiments, methods 3040 illustrated in FIG. 30B deposit andplanarize metal, polysilicon, insulator, and nanotube element layers toform nonvolatile nanotube diodes which, in this example, includemultiple vertically oriented diode and nonvolatile nanotube block (NV NTblock) switch anode-on-NT series pairs. Individual cell boundaries areformed in a single etch step, each cell having a single NV NT Diodedefined by a single trench etch step after layers, except the BL0 layer,have been deposited and planarized, in order to eliminate accumulationof individual layer alignment tolerances that would substantiallyincrease cell area. Individual cell dimensions in the X direction are F(1 minimum feature) as illustrated in FIG. 40 and corresponding FIG. 67,and also F in the Y direction as illustrated in FIG. 69 which isapproximately orthogonal to the X direction, with a periodicity in X andY directions of 2F. Hence, each cell occupies an area of approximately4F².

NV NT blocks with top (upper level) and bottom (lower level) contacts,illustrated further above in FIG. 69 by nanotube elements 4050-1 and4050-2, are further illustrated in perspective drawings in FIG. 57further above. NV NT block device structures and electrical ON/OFFswitching results are described with respect to FIGS. 64 and 65 furtherabove. Methods of fabrication of NV NT blocks with top and bottomcontacts are described with respect to methods 6600A, 6600B, and 6600Cillustrated in FIGS. 66A, 66B, and 66C, respectively. NV NT blocks withtop and bottom contacts have channel lengths L_(SW-CH) approximatelyequal to the separation between top and bottom contacts, 35 nm forexample as described further above with respect to FIGS. 64A-64C. A NVNT block switch cross section X by Y may be formed with X=Y=F, where Fis a minimum technology node dimension. For a 35 nm technology node, aNV NT block may have dimensions of 35×35×35 nm; for a 22 nm technologynode, a NV NT block may have dimensions of 22×22×35 nm, for example. Thethickness of the nanotube element need not be related in any particularway to F.

Methods fill trenches with an insulator; and then methods planarize thesurface. Then, methods deposit and pattern bit lines on the planarizedsurface.

The fabrication of vertically-oriented 3D cells illustrated in FIG. 69proceeds as follows. In some embodiments, methods deposit a word linewiring layer on the surface of insulator 6903 having a thickness of 50to 500 nm, for example. Fabrication of the vertically-oriented diodeportion of structure 6900 is the same as in FIG. 36A described furtherabove. In some embodiments, methods etch the word line wiring layer anddefine individual word lines such as word line conductors 6910-1 (WL0)and 6910-2 (WL1). Word lines such as WL0 and WL1 are used as arraywiring conductors and may also be used as near-ohmic contacts to N+ polycathode terminals of Schottky diodes.

Examples of contact and conductors materials include elemental metalssuch as Al, Au, W, Ta, Cu, Mo, Pd, Pt, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb,Sn, as well as metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW,other suitable conductors, or conductive nitrides such as TiN, oxides,or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).Insulators may be SiO₂, SiN_(x), Al₂O₃, BeO, polyimide, Mylar or othersuitable insulating material.

Next, methods form N+ polysilicon regions 6920-1 and 6920-2 to contactword line regions 6910-1 and 6920-2, respectively. N+ polysilicon istypically doped with arsenic or phosphorous to 10²⁰ dopant atoms/cm³,for example, and has a thickness of 20 to 400 nm, for example.

Next, N polysilicon regions 6925-1 and 6925-2 are formed to contact N+polysilicon regions 6920-1 and 6920-2, respectively, and may be dopedwith arsenic or phosphorus in the range of 10¹⁴ to 10¹⁷ dopant atoms/cm³for example, and may have a thickness range of 20 nm to 400 nm, forexample. N polysilicon regions 6925-1 and 6925-2 form the cathoderegions of corresponding Schottky diodes. N and N+ polysilicon regiondimensions are defined by trench etching near the end of the processflow.

Next, methods form contact regions 6930-1 and 6930-2 on N polysiliconregions 6925-1 and 6925-2, respectively. Contact regions 6930-1 and6930-2 form anode regions that complete the formation of verticallyoriented steering diode structures. Contact regions 6930-1 and 6930-2also form bottom (lower level) contacts for NV NT blocks 4050-1 and4050-2, respectively. Fabrication of the vertically-oriented diodeportion of structure 6900 is similar to methods of fabrication describedwith respect to FIG. 36A further above. While FIG. 69 illustrates ananode-on-NT type NV NT diode formed with Schottky diodes, PN or PINdiodes may be sued instead of Schottky diodes as described further abovewith respect to FIG. 36A′

In some cases conductors such as Al, Au, W, Cu, Mo, Ti, and others maybe used as both NV NT block contacts and anodes for Schottky diodes.However, in other cases, optimizing anode material for lower forwardvoltage drop and lower diode leakage is advantageous. In such an example(not shown) a sandwich may be formed with Schottky diode anode materialin contact with N polysilicon regions and NV NT block contact materialforming bottom (lower regions) contacts. Such anode materials mayinclude Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo, Na, Ni, Os, Pb, Pd,Pt, Rb, Ru, Ta, Ti, W, Zn and other elemental metals. Also, silicidessuch as CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂, and ZrSi₂ may beused. Schottky diodes formed using such metals and silicides areillustrated in the reference by NG, K. K. “Complete Guide toSemiconductor Devices”, Second Edition, John Wiley & Sons, 2002, pp.31-41, the entire contents of which are incorporated herein byreference. Examples of NV NT block contact and materials, also incontact with anode materials, include elemental metals such as Al, Au,W, Ta, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb, Sn, as well as metalalloys such as TiAu, TiCu, TiPd, PbIn, and TiW, other suitableconductors, or conductive nitrides such as TiN, oxides, or silicidessuch as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).

Next, methods form NV NT block 4050-1 and 4050-2 on the surface ofcontact regions 6930-1 and 6930-2, respectively, having the nanotubeelement length L_(SW-CH) of the NV NT blocks defined by the nanotubethickness in the vertical Z direction and X-Y cross section defined bytrench etching near the end of the process flow. Note that NV NT block4050-1 in FIG. 69 corresponds to nanotube element 4050 in FIG. 40. Inorder to maximize the density of cells C00 and C10, NV NT blocks 4050-1and 4050-2 illustrated in FIG. 69 include simple top and bottom contactswithin trench-defined cell boundaries.

Next, methods form top (upper level) contacts 4065-1 and 4065-2 on thetop surfaces of NV NT blocks 4050-1 and 4050-2, respectively, with X andY dimensions defined by trench etching near the end of the process flow.

Next, methods form (etch) trench openings 6975, 6975A, and 6975B ofwidth F thereby forming inner and outer sidewalls of cells C00 and C10and corresponding top (upper level) and bottom (lower level) contacts,nanotube elements, and insulators. Bottom (lower level) contacts 6930-1and 6930-2 form an electrical connection between NV NT blocks 4050-1 and4050-2, respectively, and also form underlying steering diode anodeterminals, and form word lines 6910-1 and 6910-2. Trench formation(etching) stops at the surface of insulator 6903.

Next, methods fill trench openings 6975, 6975A, and 6975B with aninsulator 6960, 6960A, and 6960B such as TEOS and planarize the surface.All trenches can be formed simultaneously.

Next, methods deposit and planarize a bit line layer.

Next, methods pattern bit line 6970.

Nonvolatile nanotube diodes forming cells C00 and C10 correspond tononvolatile nanotube diode 1300 schematic in FIG. 13, also illustratedschematically by NV NT diode 6980 in FIG. 69, one in each of cells C00and C10. Cells C00 and C10 illustrated in cross section 6900 in FIG. 69correspond to corresponding cells C00 and C10 shown schematically inmemory array 2910 in FIG. 29A, and word lines WL0 and WL1 and bit lineBL0 correspond to array lines illustrated schematically in memory array2910.

At this point in the process, corresponding structures in the Xdirection are formed to complete NV NT diode-based cell structures. FIG.70 illustrates cross section 7000 along word line WL0 along word line (Xaxis) direction. Stacked series-connected vertically-oriented steeringdiodes and nonvolatile nanotube block switches are symmetrical and haveapproximately the same cross sections in both X and Y directions. Crosssection 7000 illustrates array cells in which the steering diode isconnected to the bottom (lower level) contact of the nonvolatilenanotube block in an anode-on-NT configuration. Word lines are orientedalong the X axis and bit lines along the Y axis as illustrated inperspective in FIG. 33A.

Cross section 7000 illustrated in FIG. 70 illustrates support circuitsand interconnections 6901 and insulator 6903 as described further abovewith respect to FIG. 69. Cross section 7000 is in the X direction alongword line 6910-1 (WL0).

N+ polysilicon regions 6920-1′ and 6920-1″ form contacts between wordline 6910-1 (WL0) and N polysilicon regions 6925-1′ and 6925-1″,respectively, that form diode cathode regions. Bottom (lower level)contacts 6930-1′ and 6930-1″ act as anodes to form Schottky diodes withN polysilicon regions 6925-1′ and 6925-1″, respectively, as well ascontacts to nonvolatile nanotube blocks 4050-1′ and 4050-1″,respectively, as illustrated in cross section 7000 illustrated in FIG.70.

NV NT block 4050-1′ and 4050-1″ on the surface of contact regions6930-1′ and 6930-1″, respectively, have nanotube element lengthL_(SW-CH) of the NV NT blocks defined by the nanotube thickness in thevertical Z direction and X-Y cross section defined by trench etchingnear the end of the fabrication process. Note that NV NT block 4050-1′in FIG. 70 corresponds to NV NT block 4050-1 illustrated in FIG. 69. Inorder to maximize the density of cells C00 and C01 illustrated in FIG.70, NV NT blocks 4050-1′ and 4050-1″ include simple top and bottomcontacts within trench-defined cell boundaries

Contacts to the top surfaces of NV NT tubes are illustrated in FIG. 70by top (upper level) contacts 4065-1′ and 4065-1″ on the top surfaces ofNV NT blocks 4050-1′ and 4050-1″, respectively.

Bit lines 6970-1 (BL0) and 6970-2 are in direct contact with top (upperlevel) contacts 4065-1′ and 4065-1″, respectively, as illustrated inFIG. 70.

Next, methods 3050 illustrated in FIG. 30A complete fabrication ofsemiconductor chips with nonvolatile memory arrays using nonvolatilenanotube diode cell structures including passivation and packageinterconnect means using known industry methods.

Corresponding cross sections 6900 and 7000 illustrated in FIGS. 69 and70, respectively, show an anode-to-NT 3D memory array with nonvolatilenanotube block-based switches. Nanotube channel length L_(SW-CH)corresponds to NV NT diode cell dimensions in the Z direction, with X-Ycross sections with X=Y=F, as well as corresponding bit and word arraylines. Cross section 6900 is a cross section of two adjacentanode-to-nanotube type nonvolatile nanotube diode-based cells in the Ydirection that includes a NV NT block-based switch, and cross section7000 is a cross section of two adjacent anode-to-nanotube typenonvolatile nanotube diode-based cells in the X direction that includesa NV NT block-based switch. Cross sections 6900 and 7000 includecorresponding word line and bit line array lines. The nonvolatilenanotube diodes form the steering and storage elements in each cellillustrated in cross sections 6900 and 7000, and each cell has 1F by 1Fdimensions. The spacing between adjacent cells is 1F so the cellperiodicity is 2F in both the X and Y directions. Therefore one bitoccupies an area of 4F². At the 45 nm technology node, the cell area isless than about 0.01 um², or approximately 0.002 um² in this example.

Corresponding cross sections 6900 and 7000 illustrated in FIGS. 69 and70, respectively, methods of fabrication correspond to the methods offabrication described with respect to FIG. 68, except that the verticalposition of N polysilicon and N+ silicon layers are interchanged. NV NTblock switch fabrication methods of fabrication are the same. The onlydifference is that the N polysilicon layer is etched before N+polysilicon layer when forming trenches in cross sections 6900 and 7000.

Nonvolatile Memories Using NV NT Diode Device Stacks with Both SharedArray Line and Non-Shared Array Line Stacks and Cathode-to-NT SwitchConnections and Nonvolatile Nanotube Block with Top and Bottom ContactsForming 3-D NV NT Switches

FIG. 32 illustrates a method 3200 of fabricating embodiments of theinvention having two memory arrays stacked one above the other and on aninsulating layer above support circuits formed below the insulatinglayer and stacked arrays, and with communications means through theinsulating layer. While method 3200 is described further herein withrespect to nonvolatile nanotube diodes 1200 and 1300, method 3200 issufficient to cover the fabrication of many of the embodiments ofnonvolatile nanotube diodes described further above. Note also thatalthough methods 3200 are described in terms of 3D memory embodiments,methods 3200 may also be used to form 3D logic embodiments based on NVNT diodes arranged as logic arrays such as NAND and NOR arrays withlogic support circuits (instead of memory support circuits) as used inPLAs, FPGAs, and PLDs, for example.

FIG. 71 illustrates a 3D perspective drawing 7100 that includes atwo-high stack of three dimensional arrays, a lower array 7102 and anupper array 7104. Lower array 7102 includes nonvolatile nanotube diodecells C00, C01, C10, and C11. Upper array 7104 includes nonvolatilenanotube diode cells C02, C12, C03, and C13. Word lines WL0 and WL1,shared between upper and lower arrays, are oriented along the Xdirection and bit lines BL0, BL1, BL2, and BL3 are oriented along the Ydirection and are approximately orthogonal to word lines WL1 and WL2.Nanotube element channel length L_(SW-CH) is oriented vertically asshown in 3D perspective drawing 7100. Cross section 7200 correspondingto cells C00, C01, C02 and C03 is illustrated further below in FIG. 72Aand cross section 7200′ corresponding to cells C00, C02, C12, and C10are illustrated further below in FIG. 72B.

In general, methods 3210 fabricate support circuits and interconnectionsin and on a semiconductor substrate. This includes NFET and PFET deviceshaving drain, source, and gate that are interconnected to form memory(or logic) support circuits. Such structures and circuits may be formedusing known techniques that are not described in this application. Insome embodiments, methods 3210 are used to form a support circuits andinterconnections 7201 layer as part of cross sections 7200 and 7200′illustrated in FIGS. 72A and 72B using known methods of fabrication inand on which nonvolatile nanotube diode control and circuits arefabricated. Support circuits and interconnections 7201 are similar tosupport circuits and interconnections 6701 illustrated in FIGS. 67 and6901 illustrated in FIG. 69, for example, but are modified toaccommodate two stacked memory arrays. Note that while two-high stackedmemory arrays are illustrated in FIGS. 72A-72B, more than two-high 3Darray stacks may be formed (fabricated), including but not limited to4-high and 8 high stacks for example.

Next, methods 3210 are also used to fabricate an intermediate structureincluding a planarized insulator with interconnect means and nonvolatilenanotube array structures on the planarized insulator surface such asinsulator 7203 illustrated in cross sections 7200 and 7200′ in FIGS. 72Aand 72B, respectively, and are similar to insulator 6703 illustrated inFIG. 67 and insulator 6901 illustrated in FIG. 69, but are modified toaccommodate two stacked memory arrays. Interconnect means includevertically-oriented filled contacts, or studs, for interconnectingmemory support circuits in and on a semiconductor substrate below theplanarized insulator with nonvolatile nanotube diode arrays above and onthe planarized insulator surface. Planarized insulator 7203 is formedusing methods similar to methods 2730 illustrated in FIG. 27B.Interconnect means through planar insulator 7203 (not shown in crosssection 7200) are similar to contact 2807 illustrated in FIG. 28C andmay be used to connect array lines in first memory array 7210 and secondmemory array 7220 to corresponding support circuits and interconnections7201. Support circuits and interconnections 7201 and insulator 7203 formmemory array support structure 7205.

Next, methods 3220, similar to methods 2740, are used to fabricate afirst memory array 7210 using diode cathode-to-nanotube switches basedon a nonvolatile nanotube diode array similar to a nonvolatile nanotubediode array cross section 6700 illustrated in FIG. 67 and correspondingmethods of fabrication.

Next, methods 3230 similar to methods 3040 illustrated in FIG. 30B,fabricate a second memory array 7220 on the planar surface of firstmemory array 7210, but using diode anode-to-nanotube switches based on anonvolatile nanotube diode array similar to a nonvolatile nanotube diodearray cross section 6900 illustrated in FIG. 69 and correspondingmethods of fabrication

FIG. 72A illustrates cross section 7200 including first memory array7210 and second memory array 7220, with both arrays sharing word line7230 in common. Word lines such as 7230 are defined (etched) during amethods trench etch that defines memory array (cells) when forming array7220. Cross section 7200 illustrates combined first memory array 7210and second memory array 7220 in the word line, or X direction, withshared word line 7230 (WL0), four bit lines BL0, BL1, BL2, and BL3, andcorresponding cells C00, C01, C02, and C03. The array periodicity in theX direction is 2F, where F is a minimum dimension for a technology node(generation).

FIG. 72B illustrates cross section 7200′ including first memory array7210′ and second memory array 7220′ with both arrays sharing word lines7230′ and 7232 in common. Word line 7230′ is a cross sectional view ofword line 7230. Word lines such as 7230′ and 7232 are defined (etched)during a methods trench etch that defines memory array (cells) whenforming array 7220′. Cross section 7200′ illustrates combined firstmemory array 7210′ and second memory array 7220′ in the bit line, or Ydirection, with shared word lines 7230′ (WL0) and 7232 (WL1), two bitlines BL0 and BL2, and corresponding cells C00, C01, C02, and C12. Thearray periodicity in the Y direction is 2F, where F is a minimumdimension for a technology node (generation).

The memory array cell area of 1 bit for array 7210 is 4F² because of the2F periodicity in the X and Y directions. The memory array cell area of1 bit for array 7220 is 4 F² because of the 2F periodicity in the X andY directions. Because memory arrays 7220 and 7210 are stacked, thememory array cell area per bit is 2F². If four memory arrays (not shown)are stacked, then the memory array cell area per bit is 1F².

Exemplary methods 3240 using industry standard fabrication techniquescomplete fabrication of the semiconductor chip by adding additionalwiring layers as needed, and passivating the chip and adding packageinterconnect means.

In operation, memory cross section 7200 illustrated in FIG. 72A andcorresponding memory cross section 7200′ illustrated in FIG. 72Bcorrespond to the operation of memory cross section 3305 illustrated inFIG. 33B and corresponding memory cross section 3305′ illustrated inFIG. 33B′. Memory cross section 7200 and corresponding memory crosssection 7200′ operation is the same as described with respect towaveforms 3375 illustrated in FIG. 33D

FIG. 71 shows a 3D perspective drawing 7100 of a 2-high stacked arraywith shared word lines WL0 and WL1. FIG. 72A illustrates a corresponding2-high cross section 7200 in the X direction and FIG. 72B illustrates acorresponding 2-high cross section 7200′ in the Y direction. Cells C00and C01 in the lower array are formed using cathode-to-NT NV NT diodeand cells C02 and C03 in the upper array are formed using anode-to-NT NVNT diodes. An alternative stacked array structure that does not sharearray wiring, such as word lines for example, is illustrated in FIGS. 73and 74. Stacked arrays that do not share word line may use the same NVNT diode types. For example, FIGS. 73 and 74 use cathode-on-NT NV NTdiodes for both upper and lower arrays. However, anode-on-NT NV NT diodecells may be used instead. If desired, stacks may continue to use amixture of cathode-on NT and anode-on-NT NV NT diode cells. By notsharing array lines between upper and lower arrays, greater fabricationflexibility and interconnect flexibility are possible as illustratedfurther below with respect to FIGS. 75, 76A-76D, and 77.

FIG. 73 illustrates a 3D perspective drawing 7300 that includes atwo-high stack of three dimensional arrays, a lower array 7302 and anupper array 7304, with no shared (common) array lines between upperarray 7204 and lower array 7302. Word lines WL0 and WL1 oriented in theX direction and bit lines BL0 and BL1 oriented in the Y directioninterconnect cells C00, C01, C10, and C11 to form array interconnectionsfor lower array 7302. Lower array 7302 cells C00, C01, C10, and C11 areformed by cathode-on-NT NV NT diodes, however, anode-on-NT NV NT diodesmay be used instead. Word lines WL2 and WL3 oriented in the X directionand bit lines BL2 and BL3 oriented in the Y direction interconnect cellsC22, C32, C23, and C33 to form array interconnections for upper array7304. Upper array 7304 cells C22, C32, C23, and C33 are formed bycathode-on-NT NV NT diodes, however, anode-on-NT NV NT diodes may beused instead. Bit lines are approximately parallel, word lines areapproximately parallel, and bit lines and word lines are approximatelyorthogonal. Nanotube element channel length L_(SW-CH) is orientedvertically as shown in 3D perspective drawing 7300. Cross section 7400illustrated in FIG. 74 corresponding to cells C00, C01, C22, and C23 areillustrated further below in FIG. 74.

FIG. 74 illustrates cross section 7400 including first memory array 7410that includes cells C00 and C01, bit lines BL0 and BL1, and word lineWL0, and second memory array 7420 that includes cells C22 and C23, bitlines BL2 and BL3, and word line WL2. Lower array 7410 and upper array7420 are separated by insulator and interconnect region 7440 and do notshare word lines. Cross section 7400 illustrates stacked first memoryarray 7210 and second memory array 7220 in the word line, or Xdirection, with word lines WL0 and WL2, four bit lines BL0, BL1, BL2,and BL3, and corresponding cells C00, C01, C22, and C23. The arrayperiodicity in the X direction is 2F, where F is a minimum dimension fora technology node (generation). A cross section in the Y directioncorresponding to X direction cross section 7400 is not shown. However,the NV NT diode cells are symmetrical in both X and Y direction, hencethe NV NT diode cells look the same. Only the orientation of bit linesand word lines change due to a rotation by 90 degrees.

The memory array cell area of 1 bit for array 7410 is 4F² because of the2F periodicity in the X and Y directions. The memory array cell area of1 bit for array 7420 is 4F² because of the 2F periodicity in the X and Ydirections. Because memory arrays 7420 and 7410 are stacked, the memoryarray cell area per bit is 2F². If four memory arrays (not shown) arestacked, then the memory array cell area per bit is 1F².

An Alternative Simplified 3-Dimensional Cell Structure of NonvolatileCells Using NV NT Devices Having Vertically Oriented Diodes andNonvolatile Nanotube Blocks as Nonvolatile NT Switches Using Top andBottom Contacts to Form Cathode-on-NT Switches

FIG. 75 illustrates a 3-D perspective of nonvolatile memory array 7500including four 3-D nonvolatile memory cells C00, C01, C10, and C11, witheach cell including a 3-D nonvolatile nanotube diode, and cellinterconnections formed by bit lines BL0 and BL1 and word lines WL0 andWL1. Nonvolatile memory array 7500 illustrated in FIG. 75 corresponds tocross section 4000 illustrated in FIG. 40, cross section 6700illustrated in FIG. 67, and cross sections 6875 and 6890 illustrated inFIG. 68F and FIG. 68I, respectively, shown further above. The 3-D NV NTdiode dimensions used to form cells in cross sections 6700, 6875, and6890 are defined in two masking steps. First methods of masking definetrench boundaries used to form cell boundaries using directional methodsof trench etching. In some embodiments, methods of fabrication describedfurther above with respect to FIGS. 68A-68I form cell boundaries in theX direction, fill trenches with insulation, and planarize the surface.Then, second methods of masking define trenches and then methods offabrication described further above with respect to FIG. 68A-68I formcell boundaries in the Y direction, fill trenches with insulation, andplanarize the surface. Cell boundaries in the X and Y directions areapproximately orthogonal.

A memory block structure with top (upper level) and bottom (lower level)contacts illustrated in FIGS. 40, 67, and 68A-68I is symmetrical in theX and Y directions. 3-D memory arrays formed with NV NT blocks with top(upper level) and bottom (lower level) contacts enable 3-D symmetriccells, which may be leveraged to enable simplified methods offabrication to pattern and simultaneously fabricate memory arrays of 3-DNV NT diodes. X and Y direction dimensions may be definedsimultaneously, selective directional etching may be used tosimultaneously define 3-D NV NT diode cells, then fill the opening withinsulation and planarize the surface. So, for example, methods offabrication that correspond to methods of fabrication described withrespect to structures illustrated in FIG. 68D also simultaneously formthe structures illustrated in FIG. 68H. Such simplified methods offabrication facilitate multi-level array stacking because each level isfabricated with less processing steps. In this example, X=Y=F, where Fis a minimum technology dimension for a chosen technology node. Forexample, for F=45 nm technology nodes, X=Y=45 nm. The array mask designillustrated further below with respect to 76C illustrates a plan view ofF×F shapes as drawn, with each F×F shape stepped in X and Y direction bya distance F. During the process of exposing a mask layer image on thesurface of the chip, rounding of corners typically takes place atminimum technology node dimensions F, and the masking layer imagesapproximate circles of diameter F as illustrated in a plan viewillustrated further below in FIG. 76D. Because of the rounding effects,3-D NV NT diodes forming the cells of memory array 7500 will beapproximately cylindrical in shape as illustrated in FIG. 75. Memoryarray 7500 illustrated in FIG. 75 uses cathode-on-NT type of 3-D NV NTdiodes. However, anode-on-NT type of 3-D NV NT diodes such as thoseillustrated in FIGS. 69 and 70 may be formed instead.

Nonvolatile memory array methods of fabrication correspond to methods offabrication described further above with respect to FIGS. 68A-68I.However, bit line dimensions are defined prior to 3-D NV NT diode cellformation since bit lines are no longer defined by an etch step processat the same time as the definition of cell boundaries, and FIG. 68A ismodified as illustrated in FIG. 76A. Also, mask 6850 dimensionsillustrated in FIG. 68C had only the X direction equal to F. However,the Y direction was as long as the memory array or memory sub-array usedto form the memory array. Simplified methods of fabrication illustratedfurther below with respect to FIGS. 76C and 76D illustrate a mask havingthe same in X and Y directions. In some embodiments, methods offabrication corresponding to methods of fabrication described withrespect to FIGS. 68D, 68E, and 68F may be used to complete fabricationof the memory array 7500 structure.

Defining bit lines BL0 and BL1 prior to 3-D NV NT diode formationrequires that masks be aligned to pre-defined bit lines BL0 and BL1.Using semiconductor industry methods, alignment may be achieved within arange of approximately +−F/3. So, for example, for F=45 nm node, thealignment will be within +−15 nm and bit lines BL0 and BL1 are thereforein contact with most of the anode area of 3-D NV NT diodes memory cellsas illustrated further below with respect to FIG. 76B.

Support circuits & interconnections 7501 illustrated in nonvolatilememory array 7500 illustrated in FIG. 75 corresponds to support circuitsand interconnections 6701 shown in cross section 6700 illustrated inFIG. 67.

Planarized insulator 7503 illustrated in FIG. 75 corresponds toplanarized insulator 6703 illustrated in FIG. 67. Interconnect meansthrough planar insulator 7503 (not shown in cross section 7500 but shownabove with respect to cross section 2800″ in FIG. 28C) may be used toconnect metal array lines in 3-D arrays to corresponding supportcircuits and interconnections 7501. By way of example, bit line driversin BL driver and sense circuits 2640 may be connected to bit lines BL0and BL1 in array 2610 of memory 2600 illustrated in FIG. 26A describedfurther above, and in nonvolatile memory array 7500 illustrated in FIG.75.

Bit lines 7510-1 (BL0) and 7510-2 (BL1) are patterned as describedfurther below with respect to FIG. 76A. Cells C00, C01, C10, and C11 areformed by corresponding 3-D NV NT diodes that include NV NT blocks withtop (upper level) and bottom (lower level) contacts as described furtherbelow with respect to FIGS. 76A-76D.

Cell C00 includes a corresponding 3-D NV NT diode formed by a steeringdiode with a cathode-to-NT series connection to a bottom (lower level)contact of a NV NT block. Anode 7515-1 is in contact with bit line7510-1 (BL0), and the top (upper level) contact 7565-1 of NV NT block7550-1 is in contact with word line 7570-1 (WL0). The NV NT diodecorresponding to cell C00 includes anode 7515-1 in contact with bit line7510-1 (BL0), and also in contact with N polysilicon region 7520-1. Npolysilicon region 7520-1 is in contact with N+ polysilicon region7525-1. Anode 7515-1, N polysilicon region 7520-1, and N+ polysiliconregion 7525-1 form a Schottky-type of steering diode. Note that PN orPIN diodes (not shown) may be used instead. N+ polysilicon region 7525-1is in contact with bottom (lower level) contact 7530-1, which also formsthe bottom (lower level) contact of NV NT block 7550-1. NV NT block7550-1 is also in contact with top (upper level) contact 7565-1, whichis in turn in contact with word line 7570-1 (WL0). NV NT block 7550-1channel length L_(SW-CH) is vertically oriented and is approximatelyequal to the distance between top (upper level) contact 7565-1 andbottom (lower level) contact 7530-1, which may be defined by thethickness of the NV NT block.

Cell C01 includes a corresponding 3-D NV NT diode formed by a steeringdiode with a cathode-to-NT series connection to a bottom (lower level)contact of a NV NT block. Anode 7515-2 is in contact with bit line7510-2 (BL1), and the top (upper level) contact 7565-2 of NV NT block7550-2 is in contact with word line 7570-1 (WL0). The NV NT diodecorresponding to cell C01 includes anode 7515-2 in contact with bit line7510-2 (BL1), and also in contact with N polysilicon region 7520-2. Npolysilicon region 7520-2 is in contact with N+ polysilicon region7525-2. Anode 7515-2, N polysilicon region 7520-2, and N+ polysiliconregion 7525-2 form a Schottky-type of steering diode. Note that PN orPIN diodes (not shown) may be used instead. N+ polysilicon region 7525-2is in contact with bottom (lower level) contact 7530-2, which also formsthe bottom (lower level) contact of NV NT block 7550-2. NV NT block7550-2 is also in contact with top (upper level) contact 7565-2, whichis in turn in contact with word line 7570-1 (WL0). NV NT block 7550-2channel length L_(SW-CH) is vertically oriented and is approximatelyequal to the distance between top (upper level) contact 7565-2 andbottom (lower level) contact 7530-2, and may be defined by the thicknessof the NV NT block.

Cell C10 includes a corresponding 3-D NV NT diode formed by a steeringdiode with a cathode-to-NT series connection to a bottom (lower level)contact of a NV NT block. Anode 7515-3 is in contact with bit line7510-1 (BL0), and the top (upper level) contact 7565-3 of NV NT block7550-3 (not visible behind word line 7570-1) is in contact with wordline 7570-2 (WL1). The NV NT diode corresponding to cell C10 includesanode 7515-3 in contact with bit line 7510-1 (BL0), and also in contactwith N polysilicon region 7520-3. N polysilicon region 7520-3 is incontact with N+ polysilicon region 7525-3. Anode 7515-3, N polysiliconregion 7520-3, and N+ polysilicon region 7525-3 form a Schottky-type ofsteering diode. Note that PN or PIN diodes (not shown) may be usedinstead. N+ polysilicon region 7525-3 is in contact with bottom (lowerlevel) contact 7530-3, which also forms the bottom (lower level) contactof NV NT block 7550-3. NV NT block 7550-3 is also in contact with top(upper level) contact 7565-3, which is in turn in contact with word line7570-2 (WL1). NV NT block 7550-3 channel length L_(SW-CH) is verticallyoriented and is approximately equal to the distance between top (upperlevel) contact 7565-3 and bottom (lower level) contact 7530-3, and maybe defined by the thickness of NV NT block.

Cell C11 includes a corresponding 3-D NV NT diode formed by a steeringdiode with a cathode-to-NT series connection to a bottom (lower level)contact of a NV NT block. Anode 7515-4 is in contact with bit line7510-2 (BL1), and the top (upper level) contact 7565-4 of NV NT block7550-4 (not visible behind word line 7570-1) is in contact with wordline 7570-2 (WL1). The NV NT diode corresponding to cell C11 includesanode 7515-4 in contact with bit line 7510-2 (BL1), and also in contactwith N polysilicon region 7520-4. N polysilicon region 7520-4 is incontact with N+ polysilicon region 7525-4. Anode 7515-4, N polysiliconregion 7520-4, and N+ polysilicon region 7525-4 form a Schottky-type ofsteering diode. Note that PN or PIN diodes (not shown) may be usedinstead. N+ polysilicon region 7525-4 is in contact with bottom (lowerlevel) contact 7530-4, which also forms the bottom (lower level) contactof NV NT block 7550-4. NV NT block 7550-4 is also in contact with top(upper level) contact 7565-4, which is in turn in contact with word line7570-2 (WL1). NV NT block 7550-4 channel length L_(SW-CH) is verticallyoriented and is approximately equal to the distance between top (upperlevel) contact 7565-4 and bottom (lower level) contact 7530-4, and maybe defined by the thickness of the NV NT block. The opening 7575 between3-D NV NT diode-based cells C00, C01, C10, and C11 is filled with in aninsulator such as TEOS (not shown).

Nonvolatile nanotube diodes forming cells C00, C01, C10, and C11correspond to nonvolatile nanotube diode 1200 schematic in FIG. 12.Cells C00 C01, C10, and C11 illustrated in nonvolatile memory array 7500in FIG. 75 correspond to corresponding cells C00, C01, C10, and C11shown schematically in memory array 2610 in FIG. 26A, and bit lines BL0and BL1 and word lines WL0 and WL1 correspond to array lines illustratedschematically in memory array 2610.

An Alternative Simplified Methods of Fabricating 3-Dimensional CellStructure of Nonvolatile Cells Using NV NT Devices Having VerticallyOriented Diodes and Nonvolatile Nanotube Blocks as Nonvolatile NTSwitches Using Top and Bottom Contacts to Form Cathode-on-NT Switches

In some embodiments, methods 2710 illustrated in FIG. 27A are used todefine support circuits and interconnects similar to those describedwith respect to memory 2600 illustrated in FIG. 26A as described furtherabove. Exemplary methods 2710 apply known semiconductor industrytechniques design and fabrication techniques to fabricated supportcircuits and interconnections 7601 in and on a semiconductor substrateas illustrated in FIG. 76A. Support circuits and interconnections 7601include FET devices in a semiconductor substrate and interconnectionssuch as vias and wiring above a semiconductor substrate. FIG. 76Acorresponds to FIG. 34A illustrating a Schottky diode structure,including an optional conductive Schottky anode contact layer 3415 shownin FIG. 34A and shown in FIG. 76A as anode contact layer 7615. Note thatFIG. 34A′ may be used instead of FIG. 34A′ as a starting point if a PNdiode structure is desired. If N polysilicon layer 3417 in FIG. 34A′were replaced with an intrinsically doped polysilicon layer instead (notshown), then a PIN diode would be formed instead of a PN diode.Therefore, while the structure illustrated in FIG. 76A illustrates aSchottky diode structure, the structure may also be fabricated usingeither a PN diode or a PIN diode.

Methods of fabrication for elements and structures for support circuits& interconnections 7601 and insulator 7603 forming memory array supportstructure 7605 correspond to methods of fabrication described furtherabove with respect to FIGS. 34A and 34B, where support circuits &interconnections 7601 correspond to support circuits & interconnections3401; insulator 7603 corresponds to insulator 3403. Methods offabrication for elements and structures for support circuits &interconnections 7601 and insulator 7603 forming memory array supportstructure 7605 also corresponds to support circuits & interconnections6801 and insulator 7603 corresponds to insulator 6803 as illustrated inFIG. 68A, and also correspond to support circuits & interconnections7501 and insulator 7503, respectively, in FIG. 75.

At this point in the process, methods of fabrication pattern conductorlayer 7610 to form bit lines 7610-1 and bit lines 7610-2 and other bitlines separated by insulating regions 7612, as illustrated in FIG. 76A.Bit lines 7610-1 and 7610-2 correspond to bit lines 7510-1 (BL0) and7510-2 (BL1), respectively, illustrated in FIG. 75. Insulating regions7612 correspond to insulating regions 7512 illustrated in FIG. 75. Insome embodiments, methods form a masking layer (not shown) using maskingmethods known in the semiconductor industry. Next, methods such asdirectional etch define bit lines 7610-1 and 7610-2 using methods knownin the semiconductor industry. Then, methods deposit and planarize aninsulating region such as TEOS forming insulating regions 7612 usingmethods known in the semiconductor industry.

Examples of conductor (and contact) materials include elemental metalssuch as Al, Au, Pt, W, Ta, Cu, Mo, Pd, Ni, Ru, Ti, Cr, Ag, In, Ir, Pb,Sn, as well as metal alloys such as TiAu, TiCu, TiPd, PbIn, and TiW,other suitable conductors, or conductive nitrides such as TiN, oxides,or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x).

In some cases materials such as those used in conductor layer 7610 mayalso be used as anodes for Schottky diodes, in which case a separatelayer such as contact (anode) layer 7615 may not be required. In othercases, a separate contact (anode) layer 7615 may be used for enhanceddiode characteristics. For example, contact layer 3415 illustrated inFIG. 34A, corresponding to contact (anode) layer 7615 in FIG. 76A, isused to form anodes of Schottky diodes

In some embodiments, methods may deposit Schottky diode anode materialsto form contact (anode) layer 7615 on conductor layer 7610 as in FIG.76A having a thickness range of 10 to 500 nm, for example. Such anodematerials may include Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo, Na,Ni, Os, Pb, Pd, Pt, Rb, Ru, Ti, W, Ta, Zn and other elemental metals.Also, silicides such as CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂,and ZrSi₂ may be used. Schottky diodes formed using such metals andsilicides are illustrated in the reference by NG, K. K. “Complete Guideto Semiconductor Devices”, Second Edition, John Wiley & Sons, 2002, pp.31-41, the entire contents of which are incorporated herein byreference.

At this point in the process, methods deposit N polysilicon layer 7620on contact (anode) layer 7615; N+ polysilicon layer 7625 deposited on Npolysilicon layer 7620; and bottom (lower level) contact layer 7630deposited on N+ polysilicon layer 7625 as illustrated in FIG. 76A.

Exemplary methods of fabrication for N polysilicon layer 7620illustrated in FIG. 76A are described further above with respect tocorresponding N polysilicon layer 6820 illustrated in FIG. 68A andcorresponding N polysilicon layer 3420 illustrated in FIG. 34A; N+polysilicon layer 7625 corresponds to N+ polysilicon layer 6825illustrated in FIG. 68A and N+ polysilicon layer 3425 illustrated inFIG. 34A; bottom (lower level) contact layer 7630 corresponds to bottom(lower level) contact layer 6830 illustrated in FIG. 68A and bottom(lower level) contact layer 3430 illustrated in FIG. 34B.

Next, methods deposit a nanotube layer 7650 on the planar surface ofcontact (anode) layer 7630 as illustrated in FIG. 76B using spin-on ofmultiple layers, spray-on, or other means. Nanotube layer 7650 may be inthe range of 10-200 nm for example. Nanotube layer 7650 corresponds tonanotube layer 6835 illustrated in FIG. 68B. Exemplary devices of 35 nmthicknesses have been fabricated and switched between ON/OFF states asillustrated in FIGS. 64 and 65. Methods of fabrication of NV NT blockswith top and bottom contacts are described with respect to methods6600A, 6600B, and 6600C illustrated FIGS. 66A, 66B, and 66C,respectively.

At this point in the fabrication process, methods deposit top (upperlevel) contact layer 7665 on the surface of nanotube layer 7650 asillustrated in FIG. 76B. Top (upper level) contact layer 7665 may be 10to 500 nm in thickness, for example. Top (upper contact) layer 7665 maybe formed using Al, Au, Ta, W, Cu, Mo, Pd, Pt, Ni, Ru, Ti, Cr, Ag, In,Ir, Pb, Sn, as well as metal alloys such as TiAu, TiCu, TiPd, PbIn, andTiW, other suitable conductors, or conductive nitrides such as TiN,oxides, or silicides such as RuN, RuO, TiN, TaN, CoSi_(x) and TiSi_(x),for example. Top (upper level) contact layer 7665 corresponds to top(upper level) contact layer 6840 illustrated in FIG. 68B.

Next methods deposit and pattern a masking layer 7672 on top (upperlevel) contact layer 7650 as illustrated in FIG. 76B using knownindustry methods. Masking layer 7672 may be in the range of 10 to 500 nmthick and be formed using resist such as photoresist, e-beam resist, orconductor, semiconductor, or insulator materials. Mask layer 7672openings expose underlying regions for purposes of trench etching. Themask openings may be aligned to alignment marks in conductor layer 7610,methods align mask openings to an alignment accuracy AL of + or −F/3 orbetter using known semiconductor methods. For an F=45 nm technologynode, alignment AL is equal to or better than + or −15 nm with respectto a bit line edge, such as the edge of bit line 7610-1 illustrated inFIG. 76B for example. In order to achieve reduced cell dimensions, masklayer 7672 openings can be arranged to be approximately equal to theminimum allowed technology dimension F. F may be 90 nm, 65 nm, 45 nm, 35nm, 25 nm, 12 nm, or sub-10 nm for example.

FIG. 76C illustrates a plan view of masking layer 7672 with as-drawnshapes on top (upper level) contact layer 7665. Each mask pattern7672-1, 7672-2, 7672-3, and 7672-4 shape is approximately F×F as-drawn,and all shapes are separated from each other by a distance F.

FIG. 76D illustrates the effects of corner rounding when methods patternmasking regions on the surface of top (upper level) contact layer 7665at technology node minimum dimensions F using known semiconductorindustry methods. As-drawn shape 7672-1 becomes as-patternedapproximately circular shape 7672-1R of diameter approximately F;as-drawn shape 7672-2 becomes as-patterned approximately circular shape7672-2R of diameter approximately F; as-drawn shape 7672-3 becomesas-patterned approximately circular shape 7672-3R of diameterapproximately F; and as-drawn shape 7672-4 becomes as-patternedapproximately circular shape 7672-4R of diameter approximately F.

At this point in the process, methods selectively directionally etchexposed regions between mask shapes 7672-1R, 7672-2R, 7672-3R, and7672-4R, beginning with top (upper level) contact layer 7665 ending onsurface of conductor layer 7610, at the top surface of bit lines such asbit lines 7610-1 and 7610-2 thus forming opening 7675 (not shown) andsimultaneously forming all surfaces (boundaries) of 3-D NV NT diodesthat form cells C00, C01, C10, and C11 in FIG. 75. In some embodiments,methods fill opening 7675 (not shown) with an insulator such as TEOS andplanarize the surface. Opening 7675 corresponds to opening 7575 in FIG.75. If a rectangular (e.g., square) cross-section is desired, maskshapes 7672-1, 7672-2, 7672-3, and 7672-4 can be used instead of7672-1R, 7672-2R, 7672-3R, and 7672-4R.

U.S. Pat. No. 5,670,803, the entire contents of which are incorporatedherein by reference, to co-inventor Bertin, discloses a 3-D array (inthis example, 3D-SRAM) structure with simultaneously trench-definedsidewall dimensions. This structure includes vertical sidewallssimultaneously defined by trenches cutting through multiple layers ofdoped silicon and insulated regions in order avoid multiple alignmentsteps. Such trench directional selective etch methods may be adapted foruse to cut through multiple conductor, semiconductor, oxide, andnanotube layers as described further above with respect to trenchformation in FIGS. 34A-34FF, 36A-36FF, and 68A-68I for example. In thisexample, selective directional trench etch (RIE) removes exposed areasof top (upper level) contact layer 7665 to form top (upper level)contacts 7565-1, 7565-2, 7565-3, and 7565-4 illustrated in FIG. 75;removes exposed areas of nanotube layer 7650 to form NV NT blocks7550-1, 7550-2, 7550-3, and 7550-4 illustrated in FIG. 75; removesexposed areas of bottom (lower level) contact layer 7630 to form bottom(lower level) contacts 7530-1, 7530-2, 7530-3, and 7530-4 illustrated inFIG. 75; directionally etch removes exposed areas of N+ polysiliconlayer 7625 to form N+ polysilicon regions 7525-1, 7525-2, 7525-3, and7525-4 as illustrated in FIG. 75; removes exposed areas of polysiliconlayer 7620 to form N polysilicon regions 7520-1, 7520-2, 7520-3, and7520-4 as illustrated in FIG. 75. Exemplary methods of selectivedirectional etching stops at the top surface of conductor layer 7610 andtop surfaces of bit lines 7610-1 and 7610-2 as illustrated in FIGS. 76Band 75.

Exemplary methods of selectively directionally etching exposed regionsbetween mask shapes 7672-1R, 7672-2R, 7672-3R, and 7672-4R correspond tomethods of directionally etching corresponding to forming trench regionsin FIG. 68D, except that etching stops at the surface of bit lines BL0and BL1 since bit lines BL0 and BL1 have been patterned in an earlierstep as illustrated in FIG. 76B.

Next methods fill trench openings 7675 and planarize with an insulatorsuch as TEOS for example filling region 7575 (fill not shown)illustrated in FIG. 75. Exemplary methods of filling and planarizingtrench openings 7675 corresponds to methods of filling as andplanarizing trench openings 6860, 6860A, and 6860B as described withrespect to FIG. 68E.

Next, methods deposit, planarize, and pattern (form) conductors such asword lines 7570-1 (WL0) and 7570-2 (WL1) illustrated in FIG. 75.Exemplary methods of forming word lines 7570-1 and 7570-2 correspond tomethods of forming word lines WL0 and WL1 as described with respect toFIG. 68I further above.

Nonvolatile Memories Using Stacks of Alternative Simplified3-Dimensional Cell Structures with Non-Shared Array Lines

Simplified 3-dimensional nonvolatile memory array 7500 enables stackingmulti-levels of sub-arrays based on memory array 7500 to achieve highdensity bit storage per unit area. Nonvolatile memory array 7500 has acell area 4F² and a bit density of 4F²/bit. However, a 2-high stackholds two bits in the same 4F² area and achieves a bit density of2F²/bit. Likewise, a 4-high stack achieves a bit density of 1F²/bit, an8-high stack achieves a 0.5F²/bit density, and a 16-high stack achievesa 0.25F²/bit density.

FIG. 77 illustrates a schematic of stacked nonvolatile memory array 7700based on nonvolatile memory array 7500 illustrated in FIG. 75. Supportcircuits & interconnections 7701 illustrated in stacked nonvolatilememory array 7700 illustrated in FIG. 77 corresponds to support circuitsand interconnections 7501 shown in cross section 7500 illustrated inFIG. 75, except for circuit modifications to accommodate stacked arrays.BL driver and sense circuits 7705, a subset of support circuits andinterconnections 7701, are used to interface to bit lines in stackednonvolatile memory array 7700.

Planarized insulator 7707 illustrated in FIG. 77 corresponds toplanarize insulator 7503 illustrated in FIG. 75. Interconnect meansthrough planar insulator 7707 (not shown in stacked nonvolatile memoryarray 7700 but shown above with respect to cross section 2800″ in FIG.28C) may be used to connect metal array lines in 3-D arrays, bit linesin this example, to corresponding BL driver and sense circuits 7705 andother circuits (not shown). By way of example, bit line drivers in BLdriver and sense circuits 2640 may be connected to bit lines BL0 and BL1in array 2610 of memory 2600 illustrated in FIG. 26A described furtherabove, and in stacked nonvolatile memory array 7700 illustrated in FIG.77.

Three stacking levels with left and right-side 3-D sub-arrayscorresponding to nonvolatile memory array 7500 in FIG. 75 areillustrated, with additional memory stacks (not shown) above. Memoriesof 8, 16, 32, and 64 and more nonvolatile memory stacks may be formed.In this example, a first stacked memory level is formed that includesnonvolatile memory array 7710L including m×n NV NT diode cellsinterconnected by m word lines WL0_LA to WLM_LA and n bit lines BL0_LAto BLN_LA, and nonvolatile memory array 7710R including m×n NV NT diodecells interconnected by m word lines WL0_RA to WLM_RA and n bit linesBL0_RA to BLN_RA. Next, a second stacked memory level is formed thatincludes nonvolatile memory array 7720L including m×n NV NT diode cellsinterconnected by m word lines WL0_LB to WLM_LB and n bit lines BL0_LBto BLN_LB, and nonvolatile memory array 7720R including m×n NV NT diodecells interconnected by m word lines WL0_RB to WLM_RB and n bit linesBL0_RB to BLN_RB. Next, a third stacked memory level is formed thatincludes nonvolatile memory array 7730L including m×n NV NT diode cellsinterconnected by m word lines WL0_LC to WLM_LC and n bit lines BL0_LCto BLN_LC, and nonvolatile memory array 7730R including m×n NV NT diodecells interconnected by m word lines WL0_RC to WLM_RC and n bit linesBL0_RC to BLN_RC. Additional stacks of nonvolatile memory arrays areincluded (but not shown in FIG. 77).

Sub-array bit line segments are interconnected by verticalinterconnections and then fanned out to BL driver and sense circuits7705 as illustrated in stacked nonvolatile memory arrays 7700 in FIG.77. For example, BL0_L interconnects bit line BL0-LA, BL0_LB, BL0-LCsegments, and other bit line segments (not shown), and connect these bitline segments to BL driver and sense circuits 7705. Also, BLN_Linterconnects bit line BLN-LA, BLN_LB, BLN-LC segments, and other bitline segments (not shown), and connect these bit line segments to BLdriver and sense circuits 7705. Also, BL0_R interconnects bit lineBL0-RA, BL0_RB, BL0-RC segments, and other bit line segments (notshown), and connect these bit line segments to BL driver and sensecircuits 7705. Also, BLN_R interconnects bit line BLN-RA, BLN_RB, BLN-RCsegments, and other bit line segments (not shown), and connect these bitline segments to BL driver and sense circuits 7705.

BL driver and sense circuits 7705 may be used to read or write to bitlocations on any of the stacked levels in stacked nonvolatile memoryarray 7700 illustrated in FIG. 77. Word lines may also be selected bysupport circuits & interconnections 7701 (not shown in this example).

When forming nonvolatile memory arrays, annealing of polysilicon layersin the temperature range of 700 to 800 deg-C. for approximately one hourmay be required to control grain boundary size and achieve desiredelectrical parameters such as forward voltage drop and breakdownvoltages for steering diodes. For 3-D arrays, such annealing may beperformed before or after NV NT block switch formation. When stackingmemory arrays to form stacked nonvolatile memory arrays 7700, annealingin the temperature range of 700 to 800 deg-C. for one hour may berequired to improve steering diode electrical properties after NV NTblock switches are formed, because the diode layers may be arranged overthe NV NT blocks. Bottom (lower level) and top (upper level) contactmaterials may need to tolerate temperatures of up to 800 deg-C withoutforming carbides (note, nanotubes are tolerant of temperatures well inexcess of 800 deg-C.). Choosing a block contact material such as Pt canhelp to ensure that carbides do not form because Pt is insoluble incarbon. Also, choosing high melting point materials such as Mo, Cr, andNb can also avoid carbide formation. Mo and Nb carbides form above 1000deg-C., and Cr carbides form above 1200 deg-C. Other high-melting pointmetals may be used as well. By choosing contact metals that either donot form carbides, or form carbides above 800 deg-C., annealing ofstacked nonvolatile memory arrays, in which diodes are arranged aboveand/or below the NV NT blocks and their associated contacts, can beperformed without contact-to-nanotube degradation. Thus, at least someembodiments of the invention are resilient to high temperatureprocessing without degradation. Phase diagrams for various metals andcarbon may found in various references.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in respects as illustrativeand not restrictive. For example, the 3D examples described furtherabove may be used to form stand alone memory arrays. Alternatively, the3D examples described further above may be used as embedded memory inlogic chips. Also, 3D examples described further above may be stackedabove one or more microprocessors in a logic chip such that address,timing, and data line lengths are mostly vertically oriented and shortin distance for enhanced performance at lower power. Also, for example,many of the embodiments described above are described with reference tominimum technology node F. While it can be useful to fabricate memoryelements at the smallest size allowed by the minimum technology node,embodiments can be fabricated at any size allowed by the minimumtechnology node (e.g., larger than the minimum feature size).

INCORPORATED PATENT REFERENCES

The following commonly-owned patent references, referred to herein as“incorporated patent references,” describe various techniques forcreating nanotube elements (nanotube fabric articles and switches),e.g., creating and patterning nanotube fabrics, and are incorporated byreference in their entireties:

Electromechanical Memory Array Using Nanotube Ribbons and Method forMaking Same (U.S. patent application Ser. No. 09/915,093, now U.S. Pat.No. 6,919,592), filed on Jul. 25, 2001;

Electromechanical Memory Having Cell Selection Circuitry ConstructedWith Nanotube Technology (U.S. patent application Ser. No. 09/915,173,now U.S. Pat. No. 6,643,165), filed on Jul. 25, 2001;

Hybrid Circuit Having Nanotube Electromechanical Memory (U.S. patentapplication Ser. No. 09/915,095, now U.S. Pat. No. 6,574,130), filed onJul. 25, 2001;

Electromechanical Three-Trace Junction Devices (U.S. patent applicationSer. No. 10/033,323, now U.S. Pat. No. 6,911,682), filed on Dec. 28,2001;

Methods of Making Electromechanical Three-Trace Junction Devices (U.S.patent application Ser. No. 10/033,032, now U.S. Pat. No. 6,784,028),filed on Dec. 28, 2001;

Nanotube Films and Articles (U.S. patent application Ser. No.10/128,118, now U.S. Pat. No. 6,706,402), filed on Apr. 23, 2002;

Methods of Nanotube Films and Articles (U.S. patent application Ser. No.10/128,117, now U.S. Pat. No. 6,835,591), filed Apr. 23, 2002;

Methods of Making Carbon Nanotube Films, Layers, Fabrics, Ribbons,Elements and Articles (U.S. patent application Ser. No. 10/341,005),filed on Jan. 13, 2003;

Methods of Using Thin Metal Layers to Make Carbon Nanotube Films,Layers, Fabrics, Ribbons, Elements and Articles (U.S. patent applicationSer. No. 10/341,055), filed Jan. 13, 2003;

Methods of Using Pre-formed Nanotubes to Make Carbon Nanotube Films,Layers, Fabrics, Ribbons, Elements and Articles (U.S. patent applicationSer. No. 10/341,054), filed Jan. 13, 2003;

Carbon Nanotube Films, Layers, Fabrics, Ribbons, Elements and Articles(U.S. patent application Ser. No. 10/341,130), filed Jan. 13, 2003;

Non-volatile Electromechanical Field Effect Devices and Circuits UsingSame and Methods of Forming Same (U.S. patent application Ser. No.10/864,186, U.S. Patent Publication No. 2005/0062035), filed Jun. 9,2004;

Devices Having Horizontally-Disposed Nanofabric Articles and Methods ofMaking the Same, (U.S. patent application Ser. No. 10/776,059, U.S.Patent Publication No. 2004/0181630), filed Feb. 11, 2004;

Devices Having Vertically-Disposed Nanofabric Articles and Methods ofMaking the Same (U.S. patent application Ser. No. 10/776,572, now U.S.Pat. No. 6,924,538), filed Feb. 11, 2004; and

Patterned Nanoscopic Articles and Methods of Making the Same (U.S.patent application Ser. No. 10/936,119, U.S. Patent Publication No.2005/0128788).

1. A nonvolatile nanotube diode comprising: a substrate; a semiconductorelement disposed over the substrate, the semiconductor element having ananode and a cathode and capable of forming an electrically conductivepathway between the anode and the cathode; a nanotube switching elementdisposed over the semiconductor element, the nanotube switching elementcomprising a conductive contact and a nanotube fabric element capable ofa plurality of resistance states; and a conductive terminal disposed inspaced relation to the conductive contact, wherein the nanotube fabricelement is interposed between and in electrical communication with theconductive contact and the conductive contact is in electricalcommunication with the cathode; wherein in response to electricalstimuli applied to the anode and the conductive terminal, thenonvolatile nanotube diode is capable of forming an electricallyconductive pathway between the anode and the conductive terminal.
 2. Thenonvolatile nanotube diode of claim 1, wherein the anode comprises aconductor material and the cathode comprises a semiconductor material.3. The nonvolatile nanotube diode of claim 2, wherein the anode materialincludes at least one of Al, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo Na,Ni, Os, Pb, Pd, Pt, Rb, Ru, Ti, W, Zn, CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂,TiSi₂, WSi₂ and ZrSi₂.
 4. The nonvolatile nanotube diode of claim 2,wherein the semiconductor element comprises a Schottky barrier diode. 5.The nonvolatile nanotube diode of claim 1, further comprising a secondconductive terminal interposed between the substrate and the anode, thesecond conductive terminal in electrical communication with the anode,wherein in response to electrical stimuli at said second conductiveterminal and the conductive terminal, the nonvolatile nanotube diode iscapable of forming an electrically conductive pathway between saidsecond conductive terminal and the conductive terminal.
 6. Thenonvolatile nanotube diode of claim 5, wherein the anode comprises asemiconductor material of a first type and the cathode region comprisesa semiconductor material of a second type.
 7. The nonvolatile nanotubediode of claim 5, wherein the semiconductor material of the first typeis positively doped, the semiconductor material of the second type isnegatively doped, and the semiconductor element forms a PN junction. 8.The nonvolatile nanotube diode of claim 1, wherein the nanotube fabricelement is substantially vertically disposed.
 9. The nonvolatilenanotube diode of claim 1, wherein the nanotube fabric element issubstantially horizontally disposed.
 10. The nonvolatile nanotube diodeof claim 1, wherein the nanotube fabric element comprises a nonwovenmultilayered fabric.
 11. The nonvolatile nanotube diode of claim 10,wherein the nanotube fabric element has a thickness betweenapproximately 20 nm and approximately 200 nm.
 12. The nonvolatilenanotube diode of claim 10, wherein the conductive contact is disposedsubstantially coplanar to a lower surface of the nanotube fabric elementand the conductive terminal is disposed substantially coplanar to anupper surface of the nanotube fabric element.
 13. The nonvolatilenanotube diode of claim 1, wherein the semiconductor element comprises afield effect transistor.
 14. A nonvolatile nanotube diode comprising: asubstrate; a conductive terminal disposed over the substrate; asemiconductor element disposed over the conductive terminal, thesemiconductor element having a cathode and an anode and capable offorming an electrically conductive pathway between the cathode and theanode; and a nanotube switching element disposed over the semiconductorelement, the nanotube switching element comprising a conductive contactand nanotube fabric element capable of a plurality of resistance states,wherein the nanotube fabric element is interposed between and inelectrical communication with anode and the conductive contact andcathode is in electrical communication with the conductive terminal; andwherein in response to electrical stimuli applied to the anode and theconductive terminal, the nonvolatile nanotube diode is capable offorming an electrically conductive pathway between the conductiveterminal and the conductive contact.
 15. The nonvolatile nanotube diodeof claim 14, wherein the anode comprises a conductor material and thecathode comprises a semiconductor material.
 16. The nonvolatile nanotubediode of claim 15, wherein the anode material includes at least one ofAl, Ag, Au, Ca, Co, Cr, Cu, Fe, Ir, Mg, Mo Na, Ni, Os, Pb, Pd, Pt, Rb,Ru, Ti, W, Zn, CoSi₂, MoSi₂, Pd₂Si, PtSi, RbSi₂, TiSi₂, WSi₂ and ZrSi₂.17. The nonvolatile nanotube diode of claim 15, wherein thesemiconductor element comprises a Schottky barrier diode.
 18. Thenonvolatile nanotube diode of claim 14, further comprising a secondconductive terminal interposed between and providing an electricallyconductive path between the anode and the patterned region of nonwovennanotube fabric.
 19. The nonvolatile nanotube diode of claim 18, whereinthe anode comprises a semiconductor material of a first type and thecathode region comprises a semiconductor material of a second type. 20.The nonvolatile nanotube diode of claim 18, wherein the semiconductormaterial of the first type is positively doped, the semiconductormaterial of the second type is negatively doped, and the semiconductorelement forms a PN junction.
 21. The nonvolatile nanotube diode of claim14, wherein the nanotube fabric element is substantially verticallydisposed.
 22. The nonvolatile nanotube diode of claim 14, wherein thenanotube fabric element is substantially horizontally disposed.
 23. Thenonvolatile nanotube diode of claim 14, wherein the nanotube fabricelement comprises a layer of nonwoven nanotubes having a thicknessbetween approximately 0.5 and approximately 20 nanometers.
 24. Thenonvolatile nanotube diode of claim 14, wherein the nanotube fabricelement comprises a nonwoven multilayered fabric.
 25. The nonvolatilenanotube diode of claim 24, wherein the conductive contact is disposedsubstantially coplanar to a lower surface of the nanotube fabric elementand the conductive terminal is disposed substantially coplanar to anupper surface of the nanotube fabric element.
 26. The nonvolatilenanotube diode of claim 14, wherein the semiconductor element comprisesa field effect transistor.